A dispersed catalyst for catalyzing methane to olefins, 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. The dispersed catalyst contains a carrier and an active metal component with a layered structure supported on the carrier. The carrier is selected from at least one of TiO 2 , Al 2 O 3 , SiO 2 . The active metal component sequentially includes a first active metal layer containing Ag element and / or Cu element and a second active metal layer containing at least one of Group VIII metal elements. The dispersed catalyst of the present invention can effectively improve the selectivity of ethylene 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] As one of the most important basic raw materials in the field of petrochemicals, ethylene is mainly derived from petroleum hydrocarbon cracking technology. However, with the large fluctuations in oil prices, the ethylene market is heavily dependent on oil prices. At present, my country focuses on the development of non-petroleum ethylene production processes, among which the process of producing low-carbon olefins from coal via methanol has matured. However, coal chemical industry consumes a lot of water and energy in the coal gasification stage, and most coal-rich producing areas are short of water, which seriously restricts the development of coal-to-olefins. At present, with the development of combustible ice and shale gas, natural gas reserves are sufficient, and natural gas conversion and utilization technology has become a research hotspot.

[0003] The process of natural gas to ethylene is mainly carried out through anaerobic coupling and aerobic coupling. The aerobic coupling has not yet been industrialized because of the risk of explosion after the flammable gas and oxidant are mixed, and the harsh operating conditions. Anaerobic coupling is the use of natural gas to produce hydrogen and high-value-added olefins. In its traditional process, methane conversion is mainly achieved through adsorption activation coupling on the catalyst surface under high temperature and high pressure conditions. However, anaerobic coupling has many by-products and cannot be converted into ethylene in a targeted manner.

[0004] Plasma conversion of natural gas is to activate methane by electron collision under the action of electric field, and then form products through free radical collision coupling. The conversion of methane by plasma technology can be carried out at room temperature and pressure, with relatively mild operating conditions and high selectivity for specific products. The product is mainly acetylene.

[0005] CN109503310A discloses a process for preparing high-concentration acetylene and hydrogen from natural gas, which uses a plasma cracking reactor, and after high-temperature cracking and rapid cooling, a series of measures are used to separate carbon black, acetylene and hydrogen.

[0006] CN105451874A discloses a reactor for preparing ethylene from methane, comprising a plasma source and a catalyst comprising a mesoporous carrier material, wherein the methane feed obtains one or more downstream products of ethylene, hydrogen and carbon through the plasma source and the catalyst. The catalyst provided by the prior art adopts an impregnation method to add an electronic additive, thereby improving the electronic environment around the active metal Pd and significantly improving the catalyst activity. However, the catalyst provided by the prior art has the defects that the particles are easy to agglomerate during the reaction, the dispersion is poor, and it is not conducive to the long-term operation of the catalyst. Summary of the invention

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

[0008] In order to achieve the above object, the present invention provides a dispersed catalyst for catalyzing methane to olefins in a first aspect, wherein the dispersed catalyst comprises a carrier and an active metal component having a layered structure supported on the carrier, wherein the carrier is selected from TiO 2 、Al 2 O 3 、SiO 2 at least one of the above, the active metal component comprises a first active metal layer and a second active metal layer, the first active metal layer contains Ag element and / or Cu element, and the second active metal layer contains at least one of the metal elements of Group VIII; based on the total weight of the dispersed catalyst, the content of the carrier is 98.9-99.89% by weight, the total content of the active metal component calculated as oxide is 0.11-1.1% by weight, and the weight ratio of the second active metal layer to the first active metal layer calculated as oxide is 1:1-100, wherein the first active metal layer is directly loaded on the carrier, and the second active metal layer is loaded on the first active metal layer.

[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 a Cu 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) cyclically depositing a metal source II containing at least one metal element of Group VIII 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;

[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 0.11-1.1 wt % 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 1:1-100.

[0014] The catalyst described in the present invention has a stable structure, and the method of the present invention can achieve precise control of the catalyst at the nanoscale. The prepared catalyst can adapt to changes in the composition of tail gas caused by unstable discharge in the plasma process, realize methane conversion to ethylene at low temperature and normal pressure, and obtain higher ethylene 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 mentioned above, the first aspect of the present invention provides a dispersed catalyst for catalyzing methane to olefins, wherein the dispersed catalyst comprises a carrier and an active metal component having a layered structure supported on the carrier, wherein the carrier is selected from TiO 2 、Al 2 O 3 、SiO 2 at least one of the above, the active metal component comprises a first active metal layer and a second active metal layer, the first active metal layer contains Ag element and / or Cu element, and the second active metal layer contains at least one of the metal elements of Group VIII; based on the total weight of the dispersed catalyst, the content of the carrier is 98.9-99.89% by weight, the total content of the active metal component calculated as oxide is 0.11-1.1% by weight, and the weight ratio of the second active metal layer to the first active metal layer calculated as oxide is 1:1-100, wherein the first active metal layer is directly loaded on the carrier, and the second active metal layer is loaded on the first active metal layer.

[0019] Preferably, the weight ratio of the second active metal layer to the first active metal layer, respectively calculated as oxide, is 1:10-100, more preferably 1:20-50.

[0020] Preferably, based on the total weight of the dispersed catalyst, the content of the carrier is 98.9-99.4% by weight, and the total content of the active metal components calculated as oxides is 0.6-1.1% by weight.

[0021] Preferably, the second active metal layer contains at least one metal element selected from Fe, Co, Ni, Pd, Ir, and Pt.

[0022] More preferably, the second active metal layer contains at least one metal element selected from Pd, Ir, and Pt. The inventors have found that the dispersed catalyst in this preferred case has a higher ethylene selectivity.

[0023] According to a particularly preferred embodiment, the first active metal layer contains Ag element, and the second active metal layer contains Pd element; under this preferred embodiment, the dispersed catalyst has higher ethylene selectivity.

[0024] Preferably, the average particle size of the dispersed catalyst is 3-5 mm.

[0025] Preferably, the average particle size of the dispersed catalyst is 3-3.5 mm.

[0026] 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.

[0027] 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:

[0028] (1) using an atomic deposition method to cyclically deposit a metal source I containing an Ag element and / or a Cu 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;

[0029] (2) cyclically depositing a metal source II containing at least one metal element of Group VIII 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;

[0030] 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 0.11-1.1 wt % 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 1:1-100.

[0031] The present invention has no particular limitation on the duration of each cycle. Exemplarily, the duration of each cycle is 0.05-2s.

[0032] 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 0.6-1.1 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 in terms of oxide is 1:20-50, the ethylene selectivity of the obtained dispersed catalyst is higher.

[0033] Preferably, the metal source I is selected from (triethylphosphine) pivaloylsilver (Ag(Piv)(PEt 3 ))、(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)(PEt 3 )), trimethylphosphine (hexafluoroacetylacetonate) silver ((hfac)Ag(PMe 3 )), copper acetylacetonate (Cu(acac) 2 ) at least one of.

[0034] Preferably, the metal source II is at least one organic substance selected from at least one metal element of Fe, Co, Ni, Pd, Ir, and Pt.

[0035] More preferably, the metal source II is selected from at least one of an organic compound of palladium, an organic compound of iridium and an organic compound of platinum.

[0036] Particularly preferably, the metal source II is selected from palladium hexafluoroacetylacetonate (Pd(hfac) 2 )), tris(acetylacetonate)palladium (Pd(acac) 2 ), bis(1,5-cyclooctadiene)iridium chloride dimer ([Ir(cod)Cl] 2 ), bis(2-benzothiazolyl-C2,N)iridium acetylacetonate (Ir(btb) 2 (acac)), trimethyl(methylcyclopentadienyl)platinum (MeCpPtMe 3 )、(1,5-cyclooctadiene)dimethylplatinum (Pt(cod)(Me) 2 ) at least one of.

[0037] 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.

[0038] Preferably, in step (1), the number of cycles is 150-400.

[0039] Particularly preferably, in step (2), the number of cycles is 10-100.

[0040] 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.

[0041] 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.

[0042] Preferably, the first reduction reaction and the second reduction reaction are each independently in the structural formula R 1 R 2 N-NR 3 R 4 In the presence of a reducing agent, the R 1 , R 2 , R 3 , R 4 Each independently selected from H, C 1-5 Any one of the alkyl groups.

[0043] More preferably, the reducing agent is selected from at least one of anhydrous hydrazine, methylhydrazine, ethylhydrazine, propylhydrazine and tert-butylhydrazine.

[0044] Preferably, in step (1) and step (2), the pulse frequency of the reducing agent is independently 10-500 ms.

[0045] 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.

[0046] 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.

[0047] According to a particularly preferred embodiment, before each deposition is performed, the temperature of each metal source is independently 100-150°C.

[0048] 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.

[0049] According to another particularly preferred embodiment, before using at least one of the intermediate I, the intermediate II, the intermediate III and the dispersed catalyst, it is first contacted with an inert gas for cleaning.

[0050] 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.

[0051] Preferably, the inert gas is selected from at least one of argon and helium.

[0052] Preferably, the cleaning time is 1-200s.

[0053] 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, and an ALD valve.

[0054] According to a particularly preferred embodiment, the process for preparing the dispersed catalyst includes at least the following process flow:

[0055] (1) Liquid metal source I, liquid metal source II, reducing agent and a carrier to be plated are respectively placed in a metal source tank I, a metal source tank II, a reducing agent cylinder and a reaction chamber;

[0056] (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;

[0057] (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;

[0058] (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;

[0059] (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;

[0060] (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;

[0061] (7) The dispersed catalyst sample is sequentially calcined and ball-formed in an air atmosphere to obtain a dispersed catalyst.

[0062] Preferably, the calcination temperature is 400-500° C. and the calcination time is 3-6 hours.

[0063] 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.

[0064] 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.

[0065] Al 2 O 3 : Purchased from Aladdin reagent, average particle size is 3mm;

[0066] TiO 2 : Purchased from Aladdin reagent, average particle size is 3mm;

[0067] SiO 2 : Purchased from Aladdin reagent, average particle size is 3mm;

[0068] (Triethylphosphine)pivaloylsilver (Ag(Piv)(PEt 3 )):Purchased from Aladdin reagent;

[0069] Palladium hexafluoroacetylacetonate (Pd(hfac) 2 )):Purchased from Aladdin reagent;

[0070] Bis(1,5-cyclooctadiene)iridium chloride dimer ([Ir(cod)Cl] 2 ): purchased from Aladdin reagent;

[0071] (1,5-cyclooctadiene)dimethylplatinum (Pt(cod)(Me) 2 ): purchased from Aladdin reagent;

[0072] Copper acetylacetonate (Cu(acac) 2 ): purchased from Aladdin reagent;

[0073] Reducing agent (anhydrous hydrazine): purchased from Aladdin reagent;

[0074] Plasma reactor: See patent document CN109289457A, specifically, the plasma reactor includes a blade sliding arc stabilization system and a reactor:

[0075] 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;

[0076] 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.

[0077] The reaction processes in the following examples were all carried out in an ALD deposition device (model Savannah G2 ALD).

[0078] Example 1

[0079] (1) heating the metal source tank I containing the liquid silver metal source and the metal source tank II containing the liquid palladium 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;

[0080] (2) Weigh 40 g of Al 2 O 3 , mixed with anhydrous ethanol (80 ml), ultrasonically dispersed for 3 min to obtain a suspension, 2 ml of the suspension was pipetted onto a quartz plate, spread evenly, and transferred to the reaction chamber after natural drying;

[0081] (3) Open the ALD pulse valve of the metal source tank I for 100 ms to inject the liquid silver metal source (Ag(Piv)(PEt 3 )) into the reaction chamber and Al 2 O 3 The support surface undergoes self-saturation adsorption and reaction, and 200 cycles of silver metal source deposition are performed 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 seconds.

[0082] (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 a silver 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;

[0083] (5) Open the ALD pulse valve of the metal source tank II for 100ms to release the liquid palladium metal source (Pd(hfac) 2 )) is brought into the reaction chamber, undergoes self-saturation adsorption and reaction with the surface of intermediate II, and 40 cycles of palladium metal source deposition are performed to obtain 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, and the cleaning time is 100s;

[0084] (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;

[0085] (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.

[0086] Example 2

[0087] The process flow of this embodiment is the same as that of embodiment 1, except that:

[0088] An equal weight of iridium metal source ([Ir(cod)Cl] 2 ) replaces the palladium metal source (Pd(hfac) 2 )) to obtain a dispersed catalyst S2.

[0089] Example 3

[0090] The process flow of this embodiment is the same as that of embodiment 1, except that:

[0091] An equal weight of platinum metal source (Pt(cod)(Me) 2 ) replaces the palladium metal source (Pd(hfac) 2 )) to obtain dispersed catalyst S3.

[0092] Example 4

[0093] The process flow of this embodiment is the same as that of embodiment 1, except that:

[0094] With an equal weight of TiO 2 Replace Al 2 O 3 , and obtain dispersed catalyst S4.

[0095] Example 5

[0096] The process flow of this embodiment is the same as that of embodiment 1, except that:

[0097] With an equal weight of SiO 2 Replace Al 2 O 3 , and obtain dispersed catalyst S5.

[0098] Example 6

[0099] The process flow of this embodiment is the same as that of embodiment 1, except that:

[0100] Use an equal weight of copper metal source (Cu(acac) 2 ) replaces the silver metal source (Ag(Piv)(PEt 3 )) to obtain dispersed catalyst S6.

[0101] Example 7

[0102] The process flow of this embodiment is the same as that of embodiment 1, except that:

[0103] Use an equal weight of copper metal source (Cu(acac) 2 ) replaces the silver metal source (Ag(Piv)(PEt 3 )), with an equal weight of iridium metal source ([Ir(cod)Cl] 2 ) replaces the palladium metal source (Pd(hfac) 2 )) to obtain dispersed catalyst S7.

[0104] Example 8

[0105] The process flow of this embodiment is the same as that of embodiment 1, except that:

[0106] Use an equal weight of copper metal source (Cu(acac) 2 ) replaces the silver metal source (Ag(Piv)(PEt 3 )) with an equal weight of a platinum metal source (Pt(cod)(Me) 2 ) replaces the palladium metal source (Pd(hfac) 2 )) to obtain dispersed catalyst S8.

[0107] Example 9

[0108] The process flow of this embodiment is the same as that of embodiment 1, except that:

[0109] The number of cyclic depositions of the silver metal source was 300, and a dispersed catalyst S9 was obtained.

[0110] Example 10

[0111] The process flow of this embodiment is the same as that of embodiment 1, except that:

[0112] The number of cyclic depositions of the palladium metal source was 60, and a dispersed catalyst S10 was obtained.

[0113] Comparative Example 1

[0114] The process flow of this comparative example is the same as that of Example 1, except that:

[0115] Only 200 silver metal sources (Ag(Piv)(PEt 3 )) of cyclic deposition and reduction to obtain a dispersed catalyst having only a single active metal layer, specifically:

[0116] (1) The metal source tank I containing the liquid silver metal source is heated to 150° C., the reducing agent cylinder containing the reducing agent is heated to 30° C., the reaction chamber is heated to 80° C., the transport pipeline and the ALD valve are heated to 180° C., and the reaction chamber and the transport pipeline are evacuated to a pressure of 100 Pa;

[0117] (2) Weigh 40 g of Al 2 O 3 , mixed with anhydrous ethanol (80 ml), ultrasonically dispersed for 3 min to obtain a suspension, 2 ml of the suspension was pipetted onto a quartz plate, spread evenly, and transferred to the reaction chamber after natural drying;

[0118] (3) Open the ALD pulse valve of the metal source tank I for 100 ms to inject the liquid silver metal source (Ag(Piv)(PEt 3 )) into the reaction chamber and Al 2 O 3 The support surface undergoes self-saturation adsorption and reaction, and 200 cycles of silver metal source deposition are performed 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 seconds.

[0119] (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 a silver 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;

[0120] (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.

[0121] Comparative Example 2

[0122] The process flow of this comparative example is the same as that of Example 1, except that:

[0123] Only 40 palladium metal sources (Ag(Piv)(PEt 3 )) of cyclic deposition and reduction to obtain a dispersed catalyst having only a single active metal layer, specifically:

[0124] (1) Heat the metal source tank II containing the liquid palladium 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;

[0125] (2) Weigh 40 g of Al 2 O 3 , mixed with anhydrous ethanol (80 ml), ultrasonically dispersed for 3 min to obtain a suspension, 2 ml of the suspension was pipetted onto a quartz plate, spread evenly, and transferred to the reaction chamber after natural drying;

[0126] (3) Open the ALD pulse valve of the metal source tank II for 100ms to release the liquid palladium metal source (Pd(hfac) 2 )) is brought into the reaction chamber, undergoes self-saturation adsorption and reaction with the surface of intermediate II, and 40 cycles of palladium metal source deposition are performed to obtain 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, and the cleaning time is 100s;

[0127] (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;

[0128] (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.

[0129] Comparative Example 3

[0130] The process flow of this comparative example is the same as that of comparative example 2, except that:

[0131] An equal weight of iridium metal source ([Ir(cod)Cl] 2 ) replaces the palladium metal source (Pd(hfac) 2 )) to obtain dispersed catalyst D3.

[0132] Comparative Example 4

[0133] The process flow of this comparative example is the same as that of comparative example 2, except that:

[0134] An equal weight of platinum metal source (Pt(cod)(Me) 2 ) replaces the palladium metal source (Pd(hfac) 2 )) to obtain dispersed catalyst D4.

[0135] Comparative Example 5

[0136] The process flow of this comparative example is the same as that of comparative example 2, except that:

[0137] With an equal weight of TiO 2 Replace Al 2 O 3 , and obtain dispersed catalyst D5.

[0138] Test Case

[0139] Each dispersed catalyst (40 g) in the above examples was placed in a plasma reactor for reaction: the inlet flow rate was 0.5 L / min of methane, 1.5 L / min of hydrogen, and the discharge power was 120 W. The methane conversion rate and ethylene selectivity were calculated. The corresponding process conditions and results are shown in Table 1.

[0140] The methane conversion rate is calculated by the following formula:

[0141] Methane conversion rate = (methane import molar amount - methane export molar amount) / methane import molar amount.

[0142] The ethylene selectivity was calculated using the following formula:

[0143] Ethylene selectivity = (ethylene outlet molar amount)*2 / (methane inlet molar amount-methane outlet molar amount).

[0144] (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).

[0145] Table 1

[0146]

[0147]

[0148] Table 1 (continued)

[0149]

[0150] It can be seen from the results in Table 1 that the catalyst of the present invention can effectively improve the selectivity of ethylene and has broad application prospects.

[0151] 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 method for preparing a dispersed catalyst, It is characterized in that The method includes: (1) using an atomic deposition method to cyclically deposit a metal source I containing an Ag element and / or a Cu 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 metal element of Group VIII 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; Controlling the number of cycles in step (1) and step (2) so that the total content of the active metal component calculated as oxide is 0.11-1.1 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 calculated as oxide is 1:1-100; The dispersed catalyst contains a carrier and an active metal component with a layered structure supported on the carrier, and the carrier is selected from TiO 2 、Al 2 O 3 、SiO 2 at least one of the above, the active metal component comprises a first active metal layer and a second active metal layer, the first active metal layer contains Ag element and / or Cu element, and the second active metal layer contains at least one of the metal elements of Group VIII; based on the total weight of the dispersed catalyst, the content of the carrier is 98.9-99.89% by weight, the total content of the active metal component calculated as oxide is 0.11-1.1% by weight, and the weight ratio of the second active metal layer to the first active metal layer calculated as oxide is 1:1-100, wherein the first active metal layer is directly loaded on the carrier, and the second active metal layer is loaded on the first active metal layer.

2. The method according to claim 1, in, The weight ratio of the second active metal layer to the first active metal layer, calculated as oxides, is 1:10-100.

3. The method according to claim 1 or 2, in, The weight ratio of the second active metal layer to the first active metal layer, calculated as oxides, is 1:20-50.

4. The method according to claim 1 or 2, in, Based on the total weight of the dispersed catalyst, the content of the carrier is 98.9-99.4% by weight, and the total content of the active metal components calculated as oxides is 0.6-1.1% by weight.

5. The method according to claim 1 or 2, in, The second active metal layer contains at least one metal element selected from the group consisting of Fe, Co, Ni, Pd, Ir, and Pt.

6. The method according to claim 1 or 2, in, The second active metal layer contains at least one metal element selected from the group consisting of Pd, Ir, and Pt.

7. The method according to claim 1 or 2, in, The average particle size of the dispersed catalyst is 3-5 mm.

8. The method according to claim 1 or 2, in, The metal source I is selected from Ag(Piv)(PEt 3 ), (hfac)Ag(1,5-COD), Ag(fod)(PEt 3 )、(hfac)Ag(PMe 3 )、Cu(acac) 2 At least one of .

9. The method according to claim 1 or 2, in, The metal source II is at least one organic substance selected from at least one metal element among Fe, Co, Ni, Pd, Ir and Pt.

10. The method according to claim 1 or 2, in, The metal source II is selected from at least one of an organic compound of palladium, an organic compound of iridium and an organic compound of platinum.

11. The method according to claim 1 or 2, in, The metal source II is selected from (Pd(hfac) 2 )、Pd(acac) 2 、[Ir(cod)Cl] 2 、Ir(btb) 2 (acac), MeCpPtMe 3 、Pt(cod)(Me) 2 At least one of .

12. The method according to claim 1 or 2, in, In step (1) and step (2), the number of cycles is independently greater than 0 and less than or equal to 600.

13. The method according to claim 1 or 2, in, In step (1), the number of cycles is 150-400.

14. The method according to claim 1 or 2, in, In step (2), the number of cycles is 10-100.

15. The method according to claim 1 or 2, in, 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.

16. The method according to claim 1 or 2, in, In step (1) and step (2), the pulse frequencies of the metal source I and the metal source II are independently 50-2000 ms.

17. The method according to claim 1 or 2, in, The first reduction reaction and the second reduction reaction are each independently in the structure of R 1 R 2 N-NR 3 R 4 In the presence of a reducing agent, the R 1 , R 2 , R 3 , R 4 Each independently selected from H, C 1-5 Any one of the alkyl groups.

18. The method according to claim 17, in, The reducing agent is selected from at least one of anhydrous hydrazine, methyl hydrazine, ethyl hydrazine, propyl hydrazine and tert-butyl hydrazine.

19. The method according to claim 18, in, In step (1) and step (2), the pulse frequency of the reducing agent is independently 10-500 ms.

20. The method according to claim 1 or 2, in, 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.

21. The method according to claim 1 or 2, in, 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.

22. The method according to claim 1 or 2, in, Prior to each of the depositions, the temperature of each of the metal sources is independently 100-150°C.

23. The method according to claim 1 or 2, in, 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.

24. The method according to claim 23, in, The inert gas is selected from at least one of argon and helium.

25. The method according to claim 23, in, The cleaning time is 1-200s.

26. Use of the dispersed catalyst prepared by the method according to any one of claims 1 to 25 in plasma conversion of methane to olefins.

Images