CN110860309B - Dual-energy catalyst of sub-nanometer metal cobalt particles @ molecular sieve and preparation method thereof - Google Patents

Dual-energy catalyst of sub-nanometer metal cobalt particles @ molecular sieve and preparation method thereof Download PDF

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CN110860309B
CN110860309B CN201911225860.4A CN201911225860A CN110860309B CN 110860309 B CN110860309 B CN 110860309B CN 201911225860 A CN201911225860 A CN 201911225860A CN 110860309 B CN110860309 B CN 110860309B
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molecular sieve
catalyst
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metal cobalt
cobalt
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CN110860309A (en
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曹宏斌
石艳春
张计梅
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Institute of Process Engineering of CAS
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/70—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65
    • B01J29/72—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65 containing iron group metals, noble metals or copper
    • B01J29/76—Iron group metals or copper
    • B01J29/7615—Zeolite Beta
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/08—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the faujasite type, e.g. type X or Y
    • B01J29/10—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the faujasite type, e.g. type X or Y containing iron group metals, noble metals or copper
    • B01J29/14—Iron group metals or copper
    • B01J29/146—Y-type faujasite
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/40—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively
    • B01J29/42—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the pentasil type, e.g. types ZSM-5, ZSM-8 or ZSM-11, as exemplified by patent documents US3702886, GB1334243 and US3709979, respectively containing iron group metals, noble metals or copper
    • B01J29/46—Iron group metals or copper
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/70—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65
    • B01J29/72—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65 containing iron group metals, noble metals or copper
    • B01J29/76—Iron group metals or copper
    • B01J29/7676—MWW-type, e.g. MCM-22, ERB-1, ITQ-1, PSH-3 or SSZ-25
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J2229/00—Aspects of molecular sieve catalysts not covered by B01J29/00
    • B01J2229/10—After treatment, characterised by the effect to be obtained
    • B01J2229/18—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself

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Abstract

Hair brushThe invention relates to a sub-nanometer metal cobalt particle @ molecular sieve bifunctional catalyst, a preparation method and application thereof, wherein the particle size of the metal cobalt particle in the catalyst is 0.1-2nm, the metal cobalt particle is sub-nanometer, and the metal cobalt particle is uniformly distributed and uniform in particle size; the content of metallic cobalt particles in the catalyst is 0.1-5 wt%, and the molecular sieve is selected from any one of molecular sieves with FAU, MOR, BEA, MWW or MFI structures, and SiO in the molecular sieve2/Al2O35-50 percent; based on the characteristics of low melting point of cobalt nitrate and strong interaction between metal cobalt and the framework aluminum of the molecular sieve in the range of the ratio of silicon to aluminum, the invention adopts a solid-phase melting method to mix and grind the cobalt nitrate and the molecular sieve, and then the catalyst is obtained by closed heating, roasting and reducing; the preparation method of the catalyst is rapid, simple and convenient, the raw materials are easy to obtain, the cost is low, the process is environment-friendly, no water or waste liquid is generated, and the industrial operation is convenient.

Description

Dual-energy catalyst of sub-nanometer metal cobalt particles @ molecular sieve and preparation method thereof
Technical Field
The invention belongs to the field of catalytic materials, relates to a catalyst with a metal hydrogenation/dehydrogenation function and a molecular sieve acid catalysis function, and further relates to a sub-nanoscale metal cobalt particle @ molecular sieve bifunctional catalyst and a preparation method thereof.
Background
Bifunctional catalysts, which are typical representatives of catalysts, have two different catalytic active centers or catalyze two different chemical reactions to obtain target products. The concept and application of the bifunctional catalyst are distributed in various fields of petrochemical industry, new energy, organic synthesis and the like. In recent years, the development of metal/molecular sieve bifunctional catalysts becomes a research hotspot by combining the advantages of metals and molecular sieves, and the metal/molecular sieve bifunctional catalysts are applied to important reactions such as biomass catalytic conversion, phenol catalytic deoxidation, catalytic reforming and the like, and have very important significance.
The prior art reports show that: the metal/molecular sieve bifunctional catalyst is prepared mainly by adopting an impregnation method, a deposition method and an ion exchange method, so that the problems of uneven dispersion of metal particles on a molecular sieve, uneven particle size, easy agglomeration, easy loss and the like are easily caused, and finally, the stability of the catalyst is poor.
In recent years, the preparation of highly dispersed metal catalysts by a solid-phase melting method has been one of the hot points of research based on the characteristic of low melting point of nitrates.
K.P.de Jong et al prepared Mg/Cmeso catalyst with Mg particle less than 2nm by solid phase melting method (see chem.Mater.2007,19,6052-6057), and also prepared Co/SiO2And Co/Al2O3High dispersion catalysts (see document J.Catal.2013,297, 306-313; ACS Catal.2014,4, 3219-3226).
W.Z.Zhou et al introduced highly dispersed metal particles such as Co, Ni, Ce, Cr, etc. onto mesoporous materials MCM-41, SBA-15, KIT-6, etc. using a solid phase melting method (see, chem.Mater.2017,19, 2359-.
Most of the carriers introduced in the preparation process are non-acidic carriers, and the synthesized catalyst has a metal hydrogenation/dehydrogenation catalytic function, but does not have an acid catalytic function, and reports of preparing a high-dispersion metal/molecular sieve dual-functional catalyst based on the low melting point characteristic of a metal precursor and a solid-phase melting method are not provided.
Therefore, the development of the sub-nanometer metal cobalt particle catalyst with the metal hydrogenation/dehydrogenation catalytic function and the molecular sieve acid catalytic function and the preparation method thereof have important theoretical significance and practical value.
Disclosure of Invention
The invention aims to provide a sub-nano metal cobalt particle @ molecular sieve bifunctional catalyst and a preparation method thereof; the structure of the bifunctional catalyst is molecular sieve loaded metal cobalt sub-nanometer particles, the particle size of the metal cobalt particles in the bifunctional catalyst is 0.1-2nm, the particles belong to sub-nanometer level, the metal cobalt particles are uniformly distributed and uniform in particle size, the content of the metal cobalt particles in the bifunctional catalyst is 0.1-5 wt%, and the molecular sieve is selected from any one of molecular sieves with FAU, MOR, BEA, MWW or MFI structures; SiO in the molecular sieve2/Al2O35-50 percent; the bifunctional catalyst has both a metal hydrogenation/dehydrogenation function and a molecular sieve acid catalysis function, and metal cobalt particles with sub-nanometer particle sizes enable the catalyst to have higher catalytic activity in a catalytic reaction; the preparation method of the bifunctional catalyst is based on the low melting point characteristic (55 ℃) of cobalt nitrate and the ratio of metal cobalt to low silicon aluminumThe characteristic of strong interaction between Al in the sub-sieve framework adopts a solid-phase melting method, so that the bifunctional catalyst with the metal cobalt particles in sub-nanometer level is obtained.
In order to achieve the purpose, the invention adopts the following technical scheme:
in a first aspect, the present invention provides a bifunctional catalyst of sub-nanoscale metallic cobalt particles @ molecular sieve, wherein the bifunctional catalyst uses the molecular sieve as a carrier to load the metallic cobalt sub-nanoscale particles, the particle size of the metallic cobalt particles in the bifunctional catalyst is 0.1-2nm, such as 0.2nm, 0.4nm, 0.6nm, 1nm, 1.2nm, 1.4nm, 1.6nm or 1.8nm, etc., the content of the metallic cobalt particles in the bifunctional catalyst is 0.1-5 wt%, such as 0.2 wt%, 0.5 wt%, 1 wt%, 2 wt%, 3 wt% or 4 wt%, etc., and the molecular sieve is selected from any one of molecular sieves having FAU, MOR, BEA, MWW or MFI structures; SiO in the molecular sieve2/Al2O3For example, the ratio is 5 to 50, such as 10, 15, 20, 25, 30, 35, 40 or 45.
SiO in the molecular sieve herein2/Al2O3Refers to the silicon to aluminum ratio of the molecular sieve, i.e. SiO2With Al2O3In a molar ratio of (a).
Preferably, the molecular sieve is selected from molecular sieves having the structure xBEA, MWW or MFI, in which SiO is present2/Al2O320-30, for example 20, 22, 25 or 28.
In a second aspect, the invention provides a method for preparing the bifunctional catalyst of the sub-nanometer metal cobalt particle @ molecular sieve, which comprises the steps of mixing and grinding cobalt nitrate and the molecular sieve, transferring the mixture into a container with a seal, placing the container in a container with a seal, heating the container in a sealed state at 60-90 ℃, such as 65 ℃, 70 ℃, 75 ℃, 80 ℃ or 85 ℃, and taking out the container, roasting and reducing the container to obtain the bifunctional catalyst.
The preparation method of the bifunctional catalyst is based on the low melting point characteristic of cobalt nitrate and the strong interaction between metal cobalt and Al in a molecular sieve framework, controls the silicon-aluminum ratio within the range, and adopts a solid-phase melting method to form sub-nanometer metal cobalt particles on the molecular sieve. While other non-noble metal nitrates with the same lower melting point, such as nickel nitrate, undergo significant agglomeration of the metal nickel particles in the obtained catalyst during the above preparation process, and cannot reach the sub-nanometer level of the invention.
Preferably, the time of the mixed milling is 2-6h, such as 2.5, 3, 3.5, 4, 4.5, 5 or 5.5 etc., preferably 2-4 h.
Preferably, the temperature of the closed heating is 60-80 ℃, such as 65 ℃, 70 ℃, 75 ℃ or 78 ℃ and the like.
Preferably, the closed heating time is 8-24h, such as 10h, 14h, 18h or 22h, etc., preferably 12-15 h.
Preferably, the molecular sieve is selected from any one of hydrogen-type molecular sieves having the structure of BEA, MWW or MFI, wherein SiO is contained in the molecular sieve2/Al2O320-30, for example 20, 22, 25 or 28.
Preferably, the temperature of the calcination is 300-600 ℃, such as 350 ℃, 400 ℃, 500 ℃ or 600 ℃, preferably 400-500 ℃.
Preferably, the calcination time is 1 to 8 hours, such as 2 hours, 4 hours, 6 hours, 8 hours, or the like, preferably 2 to 6 hours.
Preferably, the method of reduction comprises heating the reduction under a hydrogen atmosphere.
Preferably, the temperature of the reduction is 500-700 ℃, such as 550 ℃, 600 ℃, 650 ℃ or the like.
Preferably, the reduction is carried out for a period of 4 to 10 hours, such as 5 hours, 6 hours, 7 hours, 8 hours, 10 hours, or the like.
As a preferable technical scheme, the preparation method of the sub-nanoscale metal cobalt particle @ molecular sieve bifunctional catalyst comprises the following steps:
(1) mixing and grinding cobalt nitrate and a molecular sieve for 2-6h, wherein the molecular sieve is selected from any one of hydrogen type molecular sieves with FAU, MOR, BEA, MWW or MFI structures;
(2) and (2) hermetically heating the product obtained by grinding in the step (1), wherein the heating temperature is 60-90 ℃, and the heating time is 8-24h, and then roasting and reducing to obtain the bifunctional catalyst.
Compared with the prior art, the invention has the following beneficial effects:
(1) the particle size of the metal cobalt particles in the bifunctional catalyst of the sub-nanometer metal cobalt particle @ molecular sieve is 0.1-2nm, the catalyst belongs to a sub-nanometer level, the sub-nanometer particles of the metal cobalt are uniformly distributed on the surface of the molecular sieve and have uniform particle size, the content of the metal cobalt particles in the bifunctional catalyst is 0.1-5 wt%, and the molecular sieve is selected from any one of molecular sieves with FAU, MOR, BEA, MWW or MFI structures; SiO in the molecular sieve2/Al2O3The catalyst has a metal hydrogenation/dehydrogenation function and a molecular sieve acid catalysis function;
(2) the preparation method of the bifunctional catalyst of the sub-nanometer metal cobalt particle @ molecular sieve is based on the low melting point of cobalt and the strong interaction between the metal cobalt and Al in a molecular sieve framework, and the bifunctional catalyst is prepared by adopting a solid-phase melting method, wherein the metal cobalt particles are sub-nanometer, so that the problems of large particle size, nonuniform distribution, nonuniform particle size, migration, agglomeration and loss of the metal particles in the catalyst prepared by the traditional wet impregnation method are solved.
(3) The preparation method is rapid, simple and convenient, has easily obtained raw materials, low cost, environment-friendly process, no water or waste liquid and convenient industrial operation.
Drawings
FIG. 1 is an X-ray diffraction phase diagram of the bi-functional catalyst of sub-nanoscale metallic cobalt particles @ molecular sieve prepared in example 1 of the present invention;
FIG. 2 is a transmission electron microscope image of the bifunctional catalyst of sub-nanoscale metallic cobalt particles @ molecular sieve prepared in example 1 of the present invention;
FIG. 3 is a graph showing the distribution of the particle size of metallic cobalt particles in the catalyst prepared in example 1 of the present invention;
FIG. 4 is an X-ray diffraction phase diagram of the dual-function catalyst of sub-nanometer metallic cobalt particles @ molecular sieve prepared in example 2 of the present invention;
FIG. 5 is a transmission electron microscope image of the bifunctional catalyst of sub-nanoscale metallic cobalt particles @ molecular sieve prepared in example 2 of the present invention;
FIG. 6 is a graph showing the distribution of the particle size of metallic cobalt particles in the catalyst prepared in example 2 of the present invention;
FIG. 7 is an X-ray diffraction phase diagram of the dual-function catalyst of sub-nanoscale metallic cobalt particles @ molecular sieve prepared in example 3 of the present invention;
FIG. 8 is a transmission electron microscope image of the dual-function catalyst of sub-nanometer metallic cobalt particles @ molecular sieve prepared in example 3 of the present invention;
FIG. 9 is an X-ray diffraction crystal phase diagram of the catalyst prepared in comparative example 1 of the present invention;
FIG. 10 is a transmission electron micrograph of a catalyst prepared in comparative example 1 of the present invention;
FIG. 11 is a graph showing a distribution of the particle size of metallic cobalt particles in the catalyst prepared in comparative example 1 of the present invention;
FIG. 12 is an X-ray diffraction crystal phase diagram of the catalyst prepared in comparative example 2 of the present invention;
FIG. 13 is a transmission electron micrograph of the catalyst prepared in comparative example 2 of the present invention.
FIG. 14 is a transmission electron micrograph of the catalyst prepared in comparative example 3 of the present invention.
Detailed Description
The technical solution of the present invention is further explained by the following embodiments. It should be understood by those skilled in the art that the examples are only for the understanding of the present invention and should not be construed as the specific limitations of the present invention.
In the test process, the X-ray diffraction (XRD) phase diagram of a sample is measured on a Siemens D5005 type X-ray diffractometer.
The Transmission Electron Microscope (TEM) test adopts a JEOL JEM2010F type field emission transmission electron microscope; and (3) testing conditions are as follows: and after the sample is dried, evaporating in vacuum to increase the conductivity and the contrast effect, and analyzing the accelerating voltage of the electron microscope to be 20.0kV and the magnification of 1-20K.
Example 1
The preparation method of the bifunctional catalyst of sub-nanometer metal cobalt particle @ molecular sieve (Co @ H-beta molecular sieve) in the embodiment comprises the following steps:
the molecular sieve adopted in the embodiment is an H-beta molecular sieve, the molecular sieve has a BEA structure, and SiO in the molecular sieve2/Al2O3＝25；
(1) Mixing and grinding cobalt nitrate and a molecular sieve for 3 hours to obtain a mixture, wherein the mass ratio of the molecular sieve to metal cobalt in the mixture is 1: 0.04;
(2) placing the mixture obtained in the step (1) in a conical flask, sealing the opening of the conical flask, placing the conical flask in an oven, and heating for 12 hours at 65 ℃; cooling, taking out the product, grinding, roasting at 500 ℃ for 2h, and then reducing at 500 ℃ for 4h in a hydrogen atmosphere to obtain the bifunctional catalyst of the embodiment, wherein the obtained bifunctional catalyst is A1;
the X-ray diffraction phase diagram of the bifunctional catalyst obtained in this example is shown in fig. 1, and as can be seen from fig. 1, characteristic diffraction peaks of BEA structure are observed, and the diffraction peaks of the metallic cobalt particles are not obvious; the transmission electron microscope image is shown in fig. 2, and it can be seen from fig. 2 that the particle size of the metallic cobalt particles is 0.2-1.2nm and is intensively distributed in 0.4-0.8nm, the sub-nanometer particles of the metallic cobalt are uniformly distributed and have uniform particle size, and the particle size distribution of the metallic cobalt particles is shown in fig. 3.
Example 2
The preparation method of the bifunctional catalyst of sub-nanometer metal cobalt particle @ molecular sieve (Co @ H-ZSM-5 molecular sieve) in the embodiment comprises the following steps:
this example differs from example 1 in that the molecular sieve was replaced by an H-ZSM-5 molecular sieve having the MFI structure, SiO being the molecular sieve2/Al2O3Other preparation conditions were exactly the same as in example 1, and the obtained catalyst sample was numbered a 2;
the X-ray diffraction phase diagram of the bifunctional catalyst obtained in this example is shown in fig. 4, and as can be seen from fig. 4, an MFI structural characteristic peak is observed, and there is no obvious diffraction peak of the metallic cobalt particles; the transmission electron microscope image is shown in fig. 5, and it can be seen from the image that the particle size of the metal cobalt particles is 0.4-1.4nm, the metal cobalt particles are intensively distributed at 0.7-1.1nm, the metal cobalt particles are uniformly distributed and have uniform particle size; the particle size distribution of the metallic cobalt particles is shown in fig. 6.
Example 3
The preparation method of the bifunctional catalyst of sub-nanoscale metal cobalt particles @ molecular sieve (Co @ H-MCM-22 molecular sieve) comprises the following steps:
this example differs from example 1 in that the molecular sieve was replaced with an H-MCM-22 molecular sieve having an MWW structure, in which SiO is present2/Al2O330; mixing and grinding cobalt nitrate and the MCM-22 molecular sieve for 4 hours to obtain a mixture, wherein the mass ratio of the molecular sieve to the metal cobalt in the mixture is 1: 0.02; the other preparation conditions were identical to those of example 1, and the catalyst sample obtained was designated as A3;
the X-ray diffraction crystal phase diagram of the bifunctional catalyst obtained in the example is shown in FIG. 7: the MCM-22 molecular sieve has a characteristic diffraction peak, and has no obvious diffraction peak of metal cobalt particles; the transmission electron microscope image is shown in FIG. 8: the particle size of the metal cobalt particles is 0.6-1.6nm, the metal cobalt particles are intensively distributed in 0.9-1.2nm, the metal cobalt particles are uniformly distributed, and the particle size is uniform.
Example 4
The preparation method of the bifunctional catalyst of sub-nanoscale metal cobalt particle @ molecular sieve (Co @ HY molecular sieve) in the embodiment comprises the following steps:
this example differs from example 3 in that the molecular sieve was replaced with an HY molecular sieve having an FAU structure, in which SiO was present2/Al2O320; mixing and grinding cobalt nitrate and an HY molecular sieve for 4 hours to obtain a mixture, wherein the mass ratio of the molecular sieve to metal cobalt in the mixture is 1: 0.02; the other preparation conditions were identical to those of example 1, and the catalyst sample obtained was designated as A4;
the X-ray diffraction crystal phase diagram of the bifunctional catalyst obtained in this example shows the characteristic diffraction peak of the HY molecular sieve, and there is no obvious diffraction peak of the metallic cobalt particles; the transmission electron microscope image result shows that: the particle size of the metal cobalt particles is 0.4-1.0nm, the metal cobalt particles are intensively distributed at 0.6-0.8nm, the metal cobalt particles are uniformly distributed, and the particle size is uniform.
Comparative example 1
The preparation of the catalyst in this comparative example differs from example 2 only in that the molecular sieve is replaced by an equal mass of SiO2/Al2O3H-ZSM-5 molecular sieve with MFI structure, under otherwise identical conditions as compared to example 1, the resulting catalyst sample was numbered D1;
an X-ray diffraction crystal phase diagram of the catalyst obtained in the comparative example is shown in FIG. 9, and as can be seen from FIG. 9, an MFI structural characteristic diffraction peak is observed, and no obvious diffraction peak of the metal cobalt exists, and a transmission electron microscope diagram of the catalyst is shown in FIG. 10, and as can be seen from FIG. 10, the particle size of the metal cobalt particles is 10-30nm, and the metal cobalt particles are not uniformly distributed, have non-uniform particle sizes and are mostly distributed on the outer surface of the molecular sieve; the particle size distribution of the metallic cobalt particles is shown in fig. 11.
Comparative example 2
The preparation of the catalyst in this comparative example differs from example 2 only in that the molecular sieve is replaced by an equal mass of SiO2/Al2O3H-ZSM-22 molecular sieve having the structure of TON, except under exactly the same conditions as in example 1, giving a catalyst sample numbered D2;
the X-ray diffraction phase diagram of the catalyst of the comparative example is shown in fig. 12, and as can be seen from fig. 12, a TON structure specific diffraction peak is observed, and no obvious diffraction peak of the metallic cobalt particles is observed; as shown in FIG. 13, the particle size of the cobalt metal particles is 20-30nm, and the cobalt metal particles are distributed unevenly and are distributed on the outer surface of the molecular sieve.
Comparing the particle size distribution of the metallic cobalt particles on the catalyst obtained in examples 1-2 and comparative examples 1-2, it can be seen that the present invention adopts the molecular sieve with the Si/Al ratio of 5-50 as the acidic carrier to load the metallic cobalt particles, the particle size of the metallic cobalt particles is 0.1-2nm, which is sub-nanometer, while the comparative examples 1-2 adopts the molecular sieve with the high Si/Al ratio as the carrier, and the particle size of the metallic cobalt particles on the catalyst obtained by the solid phase melting method is 10-30nm, which cannot meet the sub-nanometer requirement of the present invention.
Comparative example 3
The difference between the comparative example and the example 1 is that cobalt nitrate is replaced by nickel nitrate, the mass ratio of the molecular sieve to the metallic nickel in the mixture in the step (1) is controlled to be 1:0.04, and other conditions are completely the same as those in the example 1.
The metallic nickel particles in the catalyst obtained in this comparative example were significantly agglomerated, as shown in fig. 14, the metallic Ni particles were 10 to 30 nm.
The applicant declares that the above description is only a specific embodiment of the present invention, but the scope of the present invention is not limited thereto, and it should be understood by those skilled in the art that any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are within the scope and disclosure of the present invention.

Claims (8)

1. The bifunctional catalyst of the sub-nanometer metal cobalt particles @ molecular sieve is characterized in that the bifunctional catalyst takes the molecular sieve as a carrier to load the sub-nanometer metal cobalt particles, the particle size of the metal cobalt particles in the bifunctional catalyst is 0.1-2nm, and the content of the metal cobalt particles is 0.1-5 wt%; the molecular sieve is selected from any one of molecular sieves with FAU, MOR, BEA, MWW or MFI structure; SiO in the molecular sieve2/Al2O3＝5～50；
The preparation method of the catalyst comprises the following steps: mixing and grinding cobalt nitrate and a molecular sieve, transferring the mixture into a container with a seal, heating the mixture in a closed manner at the temperature of 60-90 ℃, taking out the mixture, and roasting and reducing the mixture to obtain the bifunctional catalyst.
2. The preparation method of the bifunctional catalyst of sub-nanometer metallic cobalt particles @ molecular sieve as claimed in claim 1, wherein the method comprises mixing and grinding cobalt nitrate and the molecular sieve, transferring into a container with a seal, heating at 60-90 ℃ in a sealed manner, taking out, and roasting and reducing to obtain the bifunctional catalyst.
3. The method of claim 2, wherein the duration of the mixed milling is between 2 and 6 hours.
4. The method of claim 3, wherein the duration of the mixed milling is 2 to 4 hours.
5. The method of claim 2, wherein the temperature of said closed heating is 60-80 ℃.
6. The method of claim 2, wherein the time for the closed heating is 8-24 hours.
7. The method of claim 6, wherein the time for the closed heating is 12-15 hours.
8. The process of any one of claims 2 to 7, wherein the molecular sieve is selected from any one of hydrogen-type molecular sieves having the structure BEA, MWW or MFI, and SiO in the molecular sieve2/Al2O3＝20～30。
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