A dispersed catalyst for catalyzing methane to olefins and its preparation method and application

Abstract

The present invention relates to the field of catalysts, and discloses a dispersed catalyst for catalyzing methane to olefins, a preparation method and an application thereof, wherein the dispersed catalyst contains a carrier and an active metal component loaded on the carrier, wherein the carrier is selected from at least one of TiO2, Al2O3 and SiO2, and the active metal component has a layered structure, and from the surface of the carrier to the outside, the active metal component sequentially contains a first active metal layer and a second active metal layer, wherein the first active metal layer contains Ag element and / or Fe element, and the second active metal layer contains at least one of Rh element, Ir element and Pt element. The dispersed catalyst of the present invention can effectively improve the selectivity of acrylic acid and has broad application prospects.

Description

Technical Field

[0001] The invention relates to the field of catalysts, and in particular to a dispersed catalyst for plasma conversion of methane to olefins and a preparation method thereof. Background Art

[0002] The development of oil and natural gas has led to the rapid development of fine chemicals. Acrylic acid, as one of the important fine chemical raw materials, is widely used in coatings, building materials, adhesives, textiles, leather, papermaking, oil production and water treatment.

[0003] The main methods for synthesizing acrylic acid include the chloroethanol method, the cyanoethanol method, the high-pressure Reppe method and the modified Reppe method, the formaldehyde-acetic acid method, the acrylonitrile hydrolysis method, the ethylene method, the propylene direct oxidation method, the propane oxidation method, and the ethylene oxide method. Among them, the only method for large-scale industrial production of acrylic acid is the two-step oxidation method using propylene as the raw material. The main raw material propylene is obtained from petroleum cracking. With the increasing shortage of petroleum resources, the cost of synthesizing acrylic acid has increased significantly.

[0004] In recent years, in addition to improving the propylene oxidation process, my country has also made certain progress in the research and development of other methods for synthesizing acrylic acid. The non-petroleum route of acetylene hydroxylation to synthesize acrylic acid does not rely on petroleum and is suitable for countries and regions that are poor in oil, rich in gas or rich in coal. my country is poor in oil and rich in coal, and has a huge production capacity of coal-to-calcium carbide. In addition, the tail gas of acetylene produced by the calcium carbide process contains a large amount of CO, which can be used as a raw material for the synthesis of acrylic acid by acetylene hydroxylation. However, coal chemical industry consumes a lot of water and energy in the coal gasification stage. Most coal-rich producing areas are short of water, which seriously restricts the development of acrylic acid produced by the acetylene process.

[0005] Currently, with the development of methane hydrate and shale gas, natural gas reserves are sufficient, and natural gas conversion and utilization technology has become a hot topic. The process of converting natural gas into acrylic acid has become a new direction for technological development.

[0006] Plasma converts natural gas, and uses electron collision to activate methane under the action of an electric field, and then free radicals collide and couple to form products. The plasma method has the characteristics of simple operation, small device size, high energy density and shortened reaction time. It can realize the conversion of natural gas at a relatively low temperature and is suitable for occasions of different scales, dispersed layouts and variable production conditions. The conversion of methane using plasma technology can be carried out at room temperature and pressure, the operating conditions are relatively mild, the selectivity of specific products is high, and the product is mainly acetylene. However, the existing plasma conversion of methane can produce a variety of products with complex components, and does not involve the method of direct plasma conversion into acrylic acid. Summary of the invention

[0007] The purpose of the present invention is to overcome the defects of low reaction efficiency of methane to olefins and low selectivity of acrylic acid in the prior art.

[0008] In order to achieve the above-mentioned purpose, the first aspect of the present invention provides a dispersed catalyst for catalyzing methane to olefins, the dispersed catalyst containing a carrier and an active metal component loaded on the carrier, the carrier is selected from at least one of TiO2, Al2O3, and SiO2, the active metal component has a layered structure, and from the surface of the carrier to the outside, the active metal component sequentially contains a first active metal layer and a second active metal layer, the first active metal layer contains Ag element and / or Fe element, and the second active metal layer contains at least one of Rh element, Ir element and Pt element; based on the total weight of the dispersed catalyst, the content of the carrier is 97-98.9% by weight, the total content of the active metal component calculated as oxide is 1.1-3% by weight, and the weight ratio of the content of the second active metal layer and the first active metal layer calculated as oxide is 1:1-20.

[0009] The second aspect of the present invention provides use of the dispersed catalyst described in the first aspect in plasma conversion of methane to olefins.

[0010] The third aspect of the present invention provides a method for preparing the dispersed catalyst according to the first aspect, the method comprising:

[0011] (1) using an atomic deposition method to cyclically deposit a metal source I containing an Ag element and / or an Fe element on a carrier to obtain an intermediate I, and subjecting the intermediate I to a first reduction reaction to obtain an intermediate II loaded with a first active metal layer;

[0012] (2) using an atomic deposition method to cyclically deposit a metal source II containing at least one of the elements Rh, Ir and Pt on the intermediate II to obtain an intermediate III, and subjecting the intermediate III to a second reduction reaction to obtain a dispersed catalyst in which a second active metal layer is supported on the first active metal layer;

[0013] The number of cycles in step (1) and step (2) is controlled so that the total content of the active metal component calculated as oxide is 1.1-3 weight % based on the total weight of the dispersed catalyst, and the weight ratio of the content of the second active metal layer and the first active metal layer calculated as oxide is 1:1-20.

[0014] The catalyst provided by the present invention has a stable structure, and the method of the present invention can realize precise control of the catalyst at the nanometer scale. The prepared catalyst is heated by the heat generated after methane is converted by plasma, and no additional heat source is required to activate the catalyst. The catalyst can adapt to the composition change of tail gas caused by unstable discharge in the plasma process, realize one-step conversion of acrylic acid at low temperature and normal pressure, and obtain higher acrylic acid selectivity. DETAILED DESCRIPTION

[0015] The endpoints and any values ​​of the ranges disclosed in this article are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of each range, the endpoint values ​​of each range and the individual point values, and the individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed in this article.

[0016] The following provides some exemplary explanations for some groups of the present invention. Unless otherwise specified, the unlisted parts are explained with reference to the following exemplary explanations.

[0017] “C 1-5 The term "alkyl" refers to an alkyl group having 1 to 5 carbon atoms, including straight-chain alkyl groups and branched-chain alkyl groups, for example, straight-chain alkyl groups and branched-chain alkyl groups having 1, 2, 3, 4, or 5 carbon atoms, for example, n-butyl, isobutyl, tert-butyl, n-pentyl, isopentyl, etc.

[0018] As described above, the first aspect of the present invention provides a dispersed catalyst for catalyzing methane to olefins, the dispersed catalyst containing a carrier and an active metal component loaded on the carrier, the carrier being selected from at least one of TiO2, Al2O3, and SiO2, the active metal component having a layered structure, and from the surface of the carrier to the outside, the active metal component sequentially contains a first active metal layer and a second active metal layer, the first active metal layer containing Ag element and / or Fe element, and the second active metal layer containing at least one of Rh element, Ir element and Pt element; based on the total weight of the dispersed catalyst, the content of the carrier is 97-98.9% by weight, the total content of the active metal component calculated as oxide is 1.1-3% by weight, and the weight ratio of the content of the second active metal layer and the first active metal layer calculated as oxide is 1:1-20.

[0019] Preferably, the weight ratio of the second active metal layer to the first active metal layer, respectively calculated as oxides, is 1:1-10, more preferably 1:1-4.

[0020] Preferably, based on the total weight of the dispersed catalyst, the content of the carrier is 97-98.5% by weight, and the total content of the active metal components calculated as oxides is 1.5-3% by weight.

[0021] Preferably, the average particle size of the dispersed catalyst is 3-5 mm.

[0022] More preferably, the average particle size of the dispersed catalyst is 3-3.5 mm.

[0023] According to a particularly preferred embodiment, the first active metal layer contains Fe, the second active metal layer contains Rh, and the content of Fe in terms of oxide is higher than that of Rh. In this preferred embodiment, the dispersed catalyst has a higher selectivity for acrylic acid.

[0024] As mentioned above, the second aspect of the present invention provides the use of the dispersed catalyst described in the first aspect in plasma conversion of methane to olefins.

[0025] As mentioned above, the third aspect of the present invention provides a method for preparing the dispersed catalyst described in the first aspect, the method comprising:

[0026] (1) using an atomic deposition method to cyclically deposit a metal source I containing an Ag element and / or an Fe element on a carrier to obtain an intermediate I, and subjecting the intermediate I to a first reduction reaction to obtain an intermediate II loaded with a first active metal layer;

[0027] (2) using an atomic deposition method to cyclically deposit a metal source II containing at least one of the elements Rh, Ir and Pt on the intermediate II to obtain an intermediate III, and subjecting the intermediate III to a second reduction reaction to obtain a dispersed catalyst in which a second active metal layer is supported on the first active metal layer;

[0028] The number of cycles in step (1) and step (2) is controlled so that the total content of the active metal component calculated as oxide is 1.1-3 weight % based on the total weight of the dispersed catalyst, and the weight ratio of the content of the second active metal layer and the first active metal layer calculated as oxide is 1:1-20.

[0029] The present invention has no particular limitation on the duration of each cycle. Exemplarily, the duration of each cycle is 0.05-2s.

[0030] In particular, the inventors have found that when the number of cycles in step (1) and step (2) is controlled so that the total content of the active metal component in terms of oxide is 1.5-3% by weight based on the total weight of the dispersed catalyst, and the weight ratio of the content of the second active metal layer to the first active metal layer in terms of oxide is 1:1-4, the obtained dispersed catalyst has a higher selectivity for acrylic acid.

[0031] Preferably, the metal source I is selected from at least one of (triethylphosphine)pivaloylsilver (Ag(Piv)(PEt3)), (1,5-cyclooctadiene)hexafluoroacetylacetonatesilver ((hfac)Ag(1,5-COD)), (triethylphosphine) (6,6,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedioic acid)silver (Ag(fod)(PEt3)), trimethylphosphine (hexafluoroacetylacetonate)silver ((hfac)Ag(PMe3)), and ferrocene (Fe(Cp)2).

[0032] Preferably, the metal source II is selected from at least one of bis(1,5-cyclooctadiene)rhodium chloride dimer ([Rh(cod)Cl]2), dicarbonyl acetylacetonate rhodium (Rh(acac)(CO)2), bis(1,5-cyclooctadiene)iridium chloride dimer ([Ir(cod)Cl]2), acetylacetonate di(2-benzothiazole-C2,N)iridium (Ir(btb)2(acac)), trimethyl(methylcyclopentadienyl)platinum (MeCpPtMe3), and (1,5-cyclooctadiene)dimethylplatinum (Pt(cod)(Me)2).

[0033] According to a preferred embodiment, in step (1) and step (2), the number of cycles is independently greater than 0 and less than or equal to 600.

[0034] Preferably, in step (1), the number of cycles is 150-400.

[0035] Particularly preferably, in step (2), the number of cycles is 10-100.

[0036] According to another preferred embodiment, in step (1) and step (2), the conditions of the atomic deposition method independently satisfy at least the following: temperature of 50-400° C., pressure of 0-200 Pa, and time of 20-800 s.

[0037] Preferably, in step (1) and step (2), the pulse frequencies of the metal source I and the metal source II are independently 50-2000 ms.

[0038] Preferably, the first reduction reaction and the second reduction reaction are each independently carried out in the presence of a reducing agent of the structural formula R1R2N-NR3R4, wherein R1, R2, R3, and R4 are each independently selected from H, C 1-5 Any one of the alkyl groups.

[0039] Preferably, the reducing agent is selected from at least one of anhydrous hydrazine, methylhydrazine, ethylhydrazine, propylhydrazine and tert-butylhydrazine.

[0040] Preferably, in step (1) and step (2), the pulse frequency of the reducing agent is independently 10-500 ms.

[0041] Preferably, in step (1), the conditions of the first reduction reaction at least meet the following conditions: temperature of 50-400° C. and pressure of 0-200 Pa.

[0042] Preferably, in step (2), the conditions of the second reduction reaction at least meet the following conditions: temperature of 50-400° C. and pressure of 0-200 Pa.

[0043] According to a particularly preferred embodiment, before each deposition is performed, the temperature of each metal source is independently 100-150°C.

[0044] According to a particularly preferred embodiment, before each of the reduction reactions is carried out, the temperature of each of the reducing agents is independently 30-70°C.

[0045] According to another particularly preferred embodiment, at least one of the intermediate I, the intermediate II, the intermediate III and the dispersed catalyst is first contacted with an inert gas for cleaning before being used.

[0046] Before applying at least one of the intermediate I, the intermediate II, the intermediate III and the dispersed catalyst, contacting with an inert gas for cleaning means: contacting the intermediate I with an inert gas for cleaning before performing the first reduction reaction; contacting the intermediate II with an inert gas for cleaning before depositing a metal source II containing at least one of the metal elements of Group VIII on the intermediate II; contacting the intermediate III with an inert gas for cleaning before performing the first reduction reaction.

[0047] Preferably, the inert gas is selected from at least one of argon and helium.

[0048] Preferably, the cleaning time is 1-200s.

[0049] According to a preferred specific embodiment, the preparation process of the dispersed catalyst is carried out in an atomic deposition device (such as an ALD deposition device), and the ALD deposition device includes a metal source tank I, a metal source tank II, a reducing agent cylinder, a reaction chamber, a transport pipeline, an ALD valve, etc.

[0050] According to a particularly preferred embodiment, the process for preparing the dispersed catalyst includes at least the following process flow:

[0051] (1) Liquid metal source I, liquid metal source II, reducing agent and a carrier to be plated are respectively placed in metal source tank I, metal source tank II, reducing agent cylinder cloth and reaction chamber;

[0052] (2) Heat each metal source tank to 140-170°C, heat the reducing agent cylinder to 30-70°C, heat the reaction chamber to 50-400°C, heat the transport pipeline and ALD valve to 180-200°C, and evacuate the reaction chamber and transport pipeline to a pressure of 10-200 Pa;

[0053] (3) Open the ALD pulse valve of the metal source tank I for 50-2000ms, cyclically bring the liquid metal source I into the reaction chamber, self-saturated adsorption occurs on the support surface, reacts and deposits to obtain the intermediate I. After the deposition is completed, an inert gas is introduced into the reaction chamber to clean the metal source that has not reacted completely and the by-products generated by the reaction. The cleaning time is 1-200s;

[0054] (4) Open the ALD pulse valve of the reducing agent cylinder for 10-500 ms to bring the reducing agent into the reaction chamber, chemically adsorb with the intermediate I and undergo a first reduction reaction to generate a reduced metal state, thereby obtaining the intermediate II. After the reaction is completed, an inert gas is introduced into the reaction chamber to clean the reducing agent that has not reacted completely and the by-products generated by the reaction. The cleaning time is 1-200 s;

[0055] (5) Open the ALD pulse valve of the metal source tank II for 50-2000 ms, cyclically bring the liquid metal source II into the reaction chamber, self-saturated adsorption occurs on the surface of the intermediate II, reacts and deposits, and obtains the intermediate III. After the deposition is completed, an inert gas is introduced into the reaction chamber to clean the metal source that has not reacted completely and the by-products generated by the reaction. The cleaning time is 1-200 s;

[0056] (6) Opening the ALD pulse valve of the reducing agent cylinder for 10-500 ms, bringing the reducing agent into the reaction chamber, chemically adsorbing with the intermediate III and undergoing a second reduction reaction to generate a reduced metal state. After the reaction is completed, an inert gas is introduced into the reaction chamber to clean the reducing agent that has not reacted completely and the by-products generated by the reaction. The cleaning time is 1-200 s to obtain a dispersed catalyst sample;

[0057] (7) The dispersed catalyst sample is sequentially calcined and ball milled to obtain a dispersed catalyst.

[0058] Preferably, the calcination is carried out in an air atmosphere, the calcination temperature is 400-500° C., and the calcination time is 3-6 hours.

[0059] It should be noted that the present invention has no particular limitation on the preparation method of the carrier to be plated, and the carrier can be prepared by methods known in the art. A specific operation is exemplified in the examples below, and those skilled in the art should not understand it as a limitation of the present invention.

[0060] The present invention will be described in detail below by way of examples. In the following examples, unless otherwise specified, all the raw materials used are commercially available products.

[0061] Al2O3: purchased from Aladdin Reagent, average particle size 3 mm;

[0062] TiO2: purchased from Aladdin Reagent, average particle size 3 mm;

[0063] Rhodium dicarbonyl acetylacetonate Rh(acac)(CO)2): purchased from Aladdin Reagent;

[0064] (Triethylphosphino)pivaloylsilver (Ag(Piv)(PEt3)): purchased from Aladdin Reagent;

[0065] Bis(1,5-cyclooctadiene)iridium chloride dimer ([Ir(cod)Cl]2): purchased from Aladdin Reagents;

[0066] (1,5-cyclooctadiene) dimethyl platinum (Pt(cod)(Me)2): purchased from Aladdin Reagents;

[0067] Ferrocene (Fe(Cp)2): purchased from Aladdin Reagent;

[0068] Reducing agent (anhydrous hydrazine): purchased from Aladdin reagent;

[0069] Plasma reactor: See patent document CN109289457A, specifically, the plasma reactor includes a blade sliding arc stabilization system and a reactor:

[0070] The blade sliding arc stabilization system comprises a first DC power supply, a second DC power supply, an inductor, a diode and an electromagnetic relay switch, wherein the first DC power supply is connected in series with the inductor and the diode, the electromagnetic relay switch is connected in series with the second DC power supply, the two series branches are connected in parallel and connected to the two electrodes of the reactor, the positive and negative poles of the two DC power supplies are in the same direction and the negative poles are grounded: the first DC power supply adopts a 1.5kV DC power supply, the second DC power supply adopts a 10kV DC power supply, and the inductor 6 adopts a 30mH inductor; the breakdown voltage is provided by the second DC power supply, and the power supply is maintained by the first DC power supply;

[0071] The reactor comprises an outer cover, two electrodes, two flat magnets and a nozzle; the electrodes are arc-shaped blade electrodes (with a radius of 20 mm), which are arranged on the lower wall plate of the reactor and are placed opposite to each other; the outer cover is a straight quadrangular prism structure with a rectangular cross-section (made of quartz, 45 mm*12 mm*110 mm, with a wall thickness of 2 mm), and two flat magnets are arranged parallel to each other on the outside of the outer cover; the nozzle (with a diameter of 2 mm) is arranged on the lower wall plate of the reactor corresponding to the middle of the two electrodes to spray gas into the reactor, and the nozzle outlet is 10 mm away from the narrowest part of the two electrodes; the upper and lower wall plates of the reactor are made of high-temperature resistant insulating material alumina ceramics, and graphite gaskets are padded between the upper and lower wall plates and the outer cover, and the upper and lower wall plates are pressed tightly by screws and nuts to fix the outer cover.

[0072] The reaction processes in the following examples were all carried out in an ALD deposition device (model Savannah G2 ALD).

[0073] Example 1

[0074] (1) heating the metal source tank I containing the liquid iron metal source and the metal source tank II containing the liquid rhodium metal source to 150° C. respectively, heating the reducing agent cylinder containing the reducing agent to 30° C., heating the reaction chamber to 80° C., heating the transport pipeline and the ALD valve to 180° C., and evacuating the reaction chamber and the transport pipeline to a pressure of 100 Pa;

[0075] (2) Weigh 40 g of Al2O3, mix with anhydrous ethanol (80 ml), and disperse by ultrasonic for 3 min to obtain a suspension. Use a dropper to draw 2 ml of the suspension and drop it onto a quartz plate. Apply it evenly, dry it naturally, and transfer it to the reaction chamber.

[0076] (3) Open the ALD pulse valve of the metal source tank I for 100 ms, bring the liquid iron metal source (Fe(Cp)2) into the reaction chamber, self-saturated adsorption and reaction with the surface of the Al2O3 carrier, and perform 200 cycles of deposition of the iron metal source to obtain intermediate I. After the deposition is completed, helium is introduced into the reaction chamber to clean the metal source that has not reacted completely and the by-products generated by the reaction. The cleaning time is 100 s;

[0077] (4) Open the ALD pulse valve of the reducing agent cylinder for 100 ms to bring the reducing agent anhydrous hydrazine into the reaction chamber, chemically adsorb and react with the intermediate I to generate a reduced metal state, and obtain the intermediate II loaded with an iron metal layer. After the reaction is completed, helium is introduced into the reaction chamber to clean the reducing agent that has not reacted completely and the by-products generated by the reaction. The cleaning time is 100 s;

[0078] (5) Open the ALD pulse valve of the metal source tank II for 100 ms, bring the liquid rhodium metal source ([Rh(cod)Cl]2) into the reaction chamber, self-saturated adsorption and reaction with the surface of the intermediate II, and perform 40 cycles of palladium metal source deposition to obtain the intermediate III. After the deposition is completed, helium is introduced into the reaction chamber to clean the metal source that has not reacted completely and the by-products generated by the reaction. The cleaning time is 100 s;

[0079] (6) Open the ALD pulse valve of the reducing agent cylinder for 100 ms to bring the reducing agent anhydrous hydrazine into the reaction chamber to chemically adsorb and react with the intermediate III to generate a reduced metal state. After the reaction is completed, helium is introduced into the reaction chamber to clean the reducing agent that has not reacted completely and the by-products generated by the reaction. The cleaning time is 100 s to obtain sample S1;

[0080] (7) Sample S1 was scraped off the quartz plate, calcined in an air atmosphere muffle furnace at 450°C for 4 h, and formed by a ball rolling machine to obtain a dispersed catalyst S1.

[0081] Example 2

[0082] The process flow of this embodiment is the same as that of embodiment 1, except that:

[0083] The rhodium metal source was replaced by an equal weight of an iridium metal source ([Ir(cod)Cl]2) to obtain a dispersed catalyst S2.

[0084] Example 3

[0085] The process flow of this embodiment is the same as that of embodiment 1, except that:

[0086] The rhodium metal source was replaced by an equal weight of a platinum metal source (Pt(cod)(Me)2) to obtain a dispersed catalyst S3.

[0087] Example 4

[0088] The process flow of this embodiment is the same as that of embodiment 1, except that:

[0089] Al2O3 was replaced by an equal weight of TiO2 to obtain dispersed catalyst S4.

[0090] Example 5

[0091] The process flow of this embodiment is the same as that of embodiment 1, except that:

[0092] By replacing Al2O3 with an equal weight of SiO2, dispersed catalyst S5 was obtained.

[0093] Example 6

[0094] The process flow of this embodiment is the same as that of embodiment 1, except that:

[0095] The iron metal source was replaced with an equal weight of a silver metal source (Ag(Piv)(PEt3)) to obtain a dispersed catalyst S6.

[0096] Example 7

[0097] The process flow of this embodiment is the same as that of embodiment 1, except that:

[0098] The iron metal source is replaced by an equal weight of a silver metal source (Ag(Piv)(PEt3)), and the rhodium metal source is replaced by an equal weight of an iridium metal source ([Ir(cod)Cl]2) to obtain a dispersed catalyst S7.

[0099] Example 8

[0100] The process flow of this embodiment is the same as that of embodiment 1, except that:

[0101] The iron metal source is replaced by an equal weight of a silver metal source (Ag(Piv)(PEt3)), and the rhodium metal source is replaced by an equal weight of a platinum metal source (Pt(cod)(Me)2) to obtain a dispersed catalyst S8.

[0102] Example 9

[0103] The process flow of this embodiment is the same as that of embodiment 1, except that:

[0104] The number of cyclic depositions of the Fe metal source was 300, and a dispersed catalyst S9 was obtained.

[0105] Example 10

[0106] The process flow of this embodiment is the same as that of embodiment 1, except that:

[0107] The number of cyclic depositions of the rhodium metal source was 80, and a dispersed catalyst S10 was obtained.

[0108] Comparative Example 1

[0109] The process flow of this comparative example is the same as that of Example 1, except that:

[0110] Only 200 cycles of deposition and reduction of the iron metal source were performed to obtain a dispersed catalyst having only a single active metal layer, specifically:

[0111] (1) Heat the metal source tank I containing the liquid iron metal source to 150° C., heat the reducing agent cylinder to 30° C., heat the reaction chamber to 80° C., heat the transport pipeline and ALD valve to 180° C., and evacuate the reaction chamber and transport pipeline to a pressure of 100 Pa;

[0112] (2) Weigh 40 g of Al2O3, mix with anhydrous ethanol (80 ml), and disperse by ultrasonic for 3 min to obtain a suspension. Use a dropper to draw 2 ml of the suspension and drop it onto a quartz plate. Apply it evenly, dry it naturally, and transfer it to the reaction chamber.

[0113] (3) Open the ALD pulse valve of the metal source tank I for 100 ms, bring the liquid iron metal source (Fe(Cp)2) into the reaction chamber, self-saturated adsorption and reaction with the surface of the Al2O3 carrier, and perform 200 cycles of deposition of the iron metal source to obtain intermediate I. After the deposition is completed, helium is introduced into the reaction chamber to clean the metal source that has not reacted completely and the by-products generated by the reaction. The cleaning time is 100 s;

[0114] (4) Open the ALD pulse valve of the reducing agent cylinder for 100 ms, bring the reducing agent anhydrous hydrazine into the reaction chamber, chemically adsorb and react with the intermediate I to generate a reduced metal state, and obtain the intermediate II loaded with an iron metal layer. After the reaction is completed, helium is introduced into the reaction chamber to clean the reducing agent that has not reacted completely and the by-products generated by the reaction. The cleaning time is 100 s, and the sample D1 is obtained;

[0115] (5) Sample D1 was scraped off the quartz plate, calcined in an air atmosphere muffle furnace at 450°C for 4 h, and formed by a ball rolling machine to obtain dispersed catalyst D1.

[0116] Comparative Example 2

[0117] The process flow of this comparative example is the same as that of Example 1, except that:

[0118] Only 40 cycles of deposition and reduction of a rhodium metal source ([Rh(cod)Cl]2) were performed to obtain a dispersed catalyst having only a single active metal layer, specifically:

[0119] (1) Heat the metal source tank II containing the liquid rhodium metal source to 150° C., heat the reducing agent cylinder containing the reducing agent to 30° C., heat the reaction chamber to 80° C., heat the transport pipeline and the ALD valve to 180° C., and evacuate the reaction chamber and the transport pipeline to a pressure of 100 Pa;

[0120] (2) Weigh 40 g of Al2O3, mix with anhydrous ethanol (80 ml), and disperse by ultrasonic for 3 min to obtain a suspension. Use a dropper to draw 2 ml of the suspension and drop it onto a quartz plate. Apply it evenly, dry it naturally, and transfer it to the reaction chamber.

[0121] (3) Open the ALD pulse valve of the metal source tank II for 100 ms, bring the liquid rhodium metal source ([Rh(cod)Cl]2) into the reaction chamber, self-saturated adsorption and reaction with the surface of the intermediate II, and perform 40 cycles of rhodium metal source deposition to obtain the intermediate III. After the deposition is completed, helium is introduced into the reaction chamber to clean the metal source that has not reacted completely and the by-products generated by the reaction. The cleaning time is 100 s;

[0122] (4) Open the ALD pulse valve of the reducing agent cylinder for 100 ms to bring the reducing agent anhydrous hydrazine into the reaction chamber to chemically adsorb and react with the intermediate III to generate a reduced metal state. After the reaction is completed, helium is introduced into the reaction chamber to clean the reducing agent that has not reacted completely and the by-products generated by the reaction. The cleaning time is 100 s to obtain sample D2;

[0123] (5) Sample D2 was scraped off the quartz plate, calcined in an air atmosphere muffle furnace at 450°C for 4 h, and formed by a ball rolling machine to obtain a dispersed catalyst D2.

[0124] Comparative Example 3

[0125] The process flow of this comparative example is the same as that of comparative example 2, except that:

[0126] The rhodium metal source was replaced by an equal weight of an iridium metal source ([Ir(cod)Cl]2) to obtain a dispersed catalyst D3.

[0127] Comparative Example 4

[0128] The process flow of this comparative example is the same as that of comparative example 2, except that:

[0129] The rhodium metal source ([Rh(cod)Cl]2) was replaced by an equal weight of a platinum metal source (Pt(cod)(Me)2) to obtain a dispersed catalyst D4.

[0130] Comparative Example 5

[0131] The process flow of this comparative example is the same as that of comparative example 2, except that:

[0132] Al2O3 was replaced by an equal weight of TiO2 to obtain dispersed catalyst D5.

[0133] Test Case

[0134] Each dispersed catalyst (40 g) in the above examples was placed in a plasma reactor for reaction: the inlet flow rate was methane 0.5 L / min, hydrogen 1.5 L / min, carbon monoxide 1.5 L / min, the discharge power was 110 W, and the methane conversion rate and acrylic acid selectivity were calculated. The corresponding process conditions and results are shown in Table 1;

[0135] The methane conversion rate is calculated by the following formula:

[0136] Methane conversion rate = (methane import molar amount - methane export molar amount) / methane import molar amount.

[0137] The acetylene selectivity is calculated by the following formula:

[0138] Acetylene selectivity = (acetylene outlet molar amount)*2 / (methane inlet molar amount-methane outlet molar amount).

[0139] The selectivity of acrylic acid is calculated by the following formula:

[0140] Acrylic acid selectivity = (acrylic acid outlet molar amount)*3 / (methane inlet molar amount-methane outlet molar amount).

[0141] (The inlet molar amount or outlet molar amount indicates the molar amount of gas taken at the inlet or outlet for one minute after the reaction is balanced).

[0142] Table 1

[0143]

[0144] Table 1 (continued)

[0145]

[0146]

[0147] It can be seen from the results in Table 1 that the catalyst of the present invention can effectively improve the selectivity of acrylic acid and has broad application prospects.

[0148] The preferred embodiments of the present invention are described in detail above, but the present invention is not limited thereto. Within the technical concept of the present invention, the technical solution of the present invention can be subjected to a variety of simple modifications, including the combination of various technical features in any other suitable manner, and these simple modifications and combinations should also be regarded as the contents disclosed by the present invention and belong to the protection scope of the present invention.

Claims

1. A dispersed catalyst for catalyzing methane to acrylic acid, characterized in that: The dispersed catalyst contains a carrier and an active metal component loaded on the carrier, the carrier is selected from at least one of TiO2, Al2O3, and SiO2, the active metal component has a layered structure, and from the surface of the carrier to the outside, the active metal component sequentially contains a first active metal layer and a second active metal layer, the first active metal layer contains Ag element and / or Fe element, and the second active metal layer contains at least one of Rh element, Ir element and Pt element; based on the total weight of the dispersed catalyst, the content of the carrier is 97-98.9% by weight, the total content of the active metal component calculated as oxide is 1.1-3% by weight, and the weight ratio of the second active metal layer to the first active metal layer calculated as oxide is 1:1-20; The dispersed catalyst is prepared by a method comprising the following steps: (1) using an atomic deposition method to cyclically deposit a metal source I containing an Ag element and / or an Fe element on a carrier to obtain an intermediate I, and subjecting the intermediate I to a first reduction reaction to obtain an intermediate II loaded with a first active metal layer; (2) cyclically depositing a metal source II containing at least one of Rh, Ir and Pt on the intermediate II by an atomic deposition method to obtain an intermediate III, and subjecting the intermediate III to a second reduction reaction to obtain a dispersed catalyst in which a second active metal layer is supported on the first active metal layer; The number of cycles in step (1) and step (2) is controlled so that the total content of the active metal component calculated as oxide is 1.1-3 wt % based on the total weight of the dispersed catalyst, and the weight ratio of the content of the second active metal layer to the first active metal layer, respectively calculated as oxide, is 1:1-20.

2. The dispersed catalyst according to claim 1, wherein The weight ratio of the second active metal layer to the first active metal layer, calculated as oxides, is 1:1-10.

3. The dispersed catalyst according to claim 2, wherein The weight ratio of the active metal component A to the active metal component B, calculated as oxides, is 1:1-4.

4. The dispersed catalyst according to any one of claims 1 to 3, wherein Based on the total weight of the dispersed catalyst, the content of the carrier is 97-98.5% by weight, and the total content of the active metal components calculated as oxides is 1.5-3% by weight.

5. The dispersed catalyst according to any one of claims 1 to 3, wherein The average particle size of the dispersed catalyst is 3-5 mm.

6. The dispersed catalyst according to any one of claims 1 to 3, wherein The metal source I is selected from at least one of Ag(Piv)(PEt3), (hfac)Ag(1,5-COD), Ag(fod)(PEt3), (hfac)Ag(PMe3), and Fe(Cp)2.

7. The dispersed catalyst according to any one of claims 1 to 3, wherein The metal source II is selected from at least one of [Rh(cod)Cl]2, Rh(acac)(CO)2, [Ir(cod)Cl]2, Ir(btb)2(acac), MeCpPtMe3, and Pt(cod)(Me)2.

8. The dispersed catalyst according to any one of claims 1 to 3, wherein In step (1) and step (2), the number of cycles is independently greater than 0 and less than or equal to 600.

9. The dispersed catalyst according to claim 8, wherein In step (1), the number of cycles is 150-400.

10. The dispersed catalyst according to claim 8, wherein In step (2), the number of cycles is 10-100.

11. The dispersed catalyst according to any one of claims 1 to 3, wherein In step (1) and step (2), the conditions of the atomic deposition method independently satisfy at least the following: temperature of 50-400° C., pressure of 0-200 Pa, and time of 20-800 s.

12. The dispersed catalyst according to any one of claims 1 to 3, wherein In step (1) and step (2), the pulse frequencies of the metal source I and the metal source II are independently 50-2000 ms.

13. The dispersed catalyst according to any one of claims 1 to 3, wherein The first reduction reaction and the second reduction reaction are each independently carried out in the presence of a reducing agent of the structural formula R1R2N-NR3R4, wherein R1, R2, R3, and R4 are each independently selected from H, C 1-5 Any one of the alkyl groups.

14. The dispersed catalyst according to claim 13, wherein The reducing agent is selected from at least one of anhydrous hydrazine, methyl hydrazine, ethyl hydrazine, propyl hydrazine and tert-butyl hydrazine.

15. The dispersed catalyst according to claim 14, wherein In step (1) and step (2), the pulse frequency of the reducing agent is independently 10-500 ms.

16. The dispersed catalyst according to any one of claims 1 to 3, wherein In step (1), the conditions of the first reduction reaction at least meet the following conditions: temperature of 50-400° C. and pressure of 0-200 Pa.

17. The dispersed catalyst according to any one of claims 1 to 3, wherein In step (2), the conditions of the second reduction reaction at least meet the following conditions: temperature of 50-400° C. and pressure of 0-200 Pa.

18. The dispersed catalyst according to any one of claims 1 to 3, wherein: Prior to each of the depositions, the temperature of each of the metal sources is independently 100-150°C.

19. The dispersed catalyst according to any one of claims 1 to 3, wherein: The method further comprises: before using at least one of the intermediate I, the intermediate II, and the intermediate III, contacting with an inert gas for cleaning.

20. The dispersed catalyst according to claim 19, wherein The inert gas is selected from at least one of argon and helium.

21. The dispersed catalyst according to claim 19, wherein The cleaning time is 1-200s.

22. Use of the dispersed catalyst according to any one of claims 1 to 21 in plasma conversion of methane to acrylic acid.

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