CN110479353B

CN110479353B - Catalyst and preparation method and application thereof

Info

Publication number: CN110479353B
Application number: CN201910729420.6A
Authority: CN
Inventors: 于吉红; 孙启明; 王宁
Original assignee: Jilin University
Current assignee: Jilin University
Priority date: 2019-08-08
Filing date: 2019-08-08
Publication date: 2020-11-27
Anticipated expiration: 2039-08-08
Also published as: CN110479353A

Abstract

The application discloses a catalyst and a preparation method and application thereof, wherein the catalyst comprises a carrier and an active component; the carrier is a pure silicon molecular sieve; the active element in the active component comprises Pt; wherein Pt is loaded in the carrier in the form of a sub-nano Pt cluster (the number of Pt atoms in the cluster is 1-10, and the average number of Pt atoms is 3); zn is linked with the carrier through a Zn-O-Si bond in the form of a single-site + 2-valent Zn ion and is connected with the platinum cluster through a Zn-O-Pt bond. The preparation method of the catalyst adopts direct hydrogen reduction, and the prepared catalyst is prepared by sub-nanometer platinum clusters and single-site Zn²⁺The ions are packaged into the pure silicon molecular sieve, and the pure silicon molecular sieve is applied to propane dehydrogenation catalytic reaction, and shows performance far exceeding that of other catalysts.

Description

Catalyst and preparation method and application thereof

Technical Field

The application relates to a catalyst, a preparation method and application thereof, and belongs to the field of catalysts.

Background

Propylene is one of the most important feedstocks in global business and is vital to the production of a variety of valuable chemicals, commodities, and fuels. Propane Dehydrogenation (PDH) is becoming increasingly popular due to the scarcity of fossil fuels and the discovery of shale gas, and is considered a more promising process to meet the increasing worldwide demand for propylene. Platinum-based catalysts are widely used in industrial PDH processes, but platinum-based catalysts tend to have the disadvantages of rapid deactivation and undesirable propylene selectivity. The size of the metal nanoparticles is a key factor influencing PDH conversion, and the reduction of the particle size is beneficial to exposing more metal active sites, so that the conversion rate of propane is improved. Al (Al)₂O₃、SiO₂The like are the most commonly used carriers for supporting platinum species, but during high temperature conversion of PDH, severe sintering of small size platinum species occurs to rapidly reduce activity.

Molecular sieves with ordered microporous structures are considered ideal supports for anchoring metal nanoparticles. However, the conventional impregnation method for supporting metal particles on a molecular sieve generally produces large-sized metal particles having poor dispersibility. Recently, Iglesia and colleagues have adopted a ligand stabilization method to limit metal nanoparticles larger than 1nm in an aluminum-silicon molecular sieve with acidity, and have shown good sintering resistance. However, for propane dehydrogenation reactions, those formed by the incorporation of aluminum into the molecular sieve

Acid, has a negative effect on propylene selectivity. Corma and colleagues prepare small-size platinum clusters in a pure silicon molecular sieve by a method of converting a two-dimensional structure into a three-dimensional MWW molecular sieve. Although the catalyst shows excellent catalytic performances such as hydrogenation and dehydrogenation, the selectivity and thermal stability of propylene are poor. The preparation of supported bimetallic catalysts by alloying platinum with various metal elements (such as tin, gallium, copper, zinc, etc.) is considered to be an effective strategy for improving the stability of platinum-based catalysts and the selectivity of propylene in PDH conversion, but the stability and catalytic efficiency of such catalysts still need to be improved.

In addition, when people prepare the metal-loaded molecular sieve catalyst by an in-situ synthesis method, the calcination-reduction process is adopted: the method comprises the steps of firstly calcining in air or oxygen to remove organic matters such as a template agent, a ligand and the like, and then reducing in a hydrogen atmosphere to obtain zero-valent metal, however, in the calcining-reducing process, metal atoms are easy to sinter and agglomerate in a molecular sieve, and the size of the metal is large.

Disclosure of Invention

According to one aspect of the present application, a catalyst is provided that encapsulates sub-nano Pt clusters (average Pt atomic number 3) into pure silica molecular sieves for propane dehydrogenation catalytic reactions, exhibiting performance far exceeding that of other catalysts.

The catalyst is characterized by comprising a carrier and an active component;

the carrier is a pure silicon molecular sieve;

the active element in the active component comprises Pt; wherein Pt is supported in the support in the form of sub-nano Pt clusters.

The sub-nano Pt cluster: the number of Pt atoms in the cluster is 1-10, and the average number of Pt atoms is 3.

Optionally, the pure silicon molecular sieve comprises at least one of a Silicalite-1 molecular sieve, a Beta molecular sieve.

Alternatively, the pure silicon molecular sieve is a Silicalite-1 molecular sieve.

Optionally, the size of the metal in the catalyst is less than 1 nm.

Optionally, the size of the metal in the catalyst is less than 0.6 nm.

The loading amount of active elements in the catalyst is 0.3-1 wt%.

Wherein, the loading amount refers to the mass percentage of the active metal element Pt in the catalyst.

Optionally, the loading amount of the active elements in the catalyst is 0.35-0.95 wt%.

Alternatively, the upper limit of the loading of active element in the catalyst is selected from 0.55 wt%, 0.75 wt% or 0.95 wt%; the lower limit is selected from 0.35 wt%, 0.55 wt% or 0.75 wt%.

Optionally, other elements are also included in the catalyst;

the other elements are non-noble metal elements;

the non-noble metal comprises Zn; the non-noble metal element exists in a + 2-valent Zn ion form and is connected with Si atoms on the framework through oxygen atoms to form a single-site structure.

Optionally, the other element is an inactive element.

Optionally, the molar ratio of the other element to the active element is 0-4: 1.

Wherein, when the other element than the active element is present in the catalyst, the end point value of the molar ratio of the other element to the active element is not 0.

Alternatively, the catalyst has the general formula:

PtM_x@ Q formula I

Wherein M is other elements;

x＝0～4；

q is a pure silicon molecular sieve.

Alternatively, x in formula I is 1, 2, 3 or 4.

The "@" in the formula I is PtMx loaded in the pure silicon molecular sieve crystal.

As a specific embodiment, the monodisperse M stable sub-nanometer Pt cluster (the Pt atom number in the cluster is 1-10, and the average Pt atom number is 3) is encapsulated in the pure silicon molecular sieve crystal.

Optionally, the catalyst is: the pure silicon molecular sieve loads single-site non-noble metal ions and sub-nanometer platinum clusters; the non-noble metal element is Zn.

Optionally, the catalyst is: single site Zn (II) ion stabilized sub-nano Pt clusters are encapsulated into pure silicon molecular sieves (Silicalite-1, Beta, etc.).

In another aspect of the present application, there is provided a method for preparing the catalyst described in any one of the above, comprising:

(1) carrying out hydrothermal crystallization on a mixture containing a metal source and a pure silicon molecular sieve preparation raw material to obtain a precursor I;

(2) heating and reducing the precursor I in a hydrogen-containing atmosphere to obtain the catalyst;

wherein the metal source is a metal complex.

Optionally, the metal source in step (1) comprises a metal source corresponding to the active element.

Optionally, the metal source in step (1) includes a metal source corresponding to the active element and a metal source corresponding to the other element.

Alternatively, the metal complex in step (1) comprises a metal complex of an active element; or

The metal complexes include metal complexes of active elements and metal complexes of other elements.

Alternatively, the metal complex is selected from [ T (NH)₂CH₂CH₂NH₂)₂]Cl₂、[T(NH₂CH₂CH₂NH₂)₂](NO₃)₂、[T(NH₂CH₂CH₂NH₂)₂](OAc)₂、[T(NH₂CH₂CH₂NH₂)₂]SO₄At least one of;

wherein T is a metal element.

Optionally, T is an active element or other element.

Optionally, T is Pt, Zn.

Alternatively, the metal complex [ T (NH)₂CH₂CH₂NH₂)₂]²⁺The preparation method comprises the following steps: and adding the metal salt corresponding to the T into the mixed solution of the ethylenediamine and the water, and stirring to obtain the complex.

Optionally, the stirring condition is stirring for 1-5 hours at 25-80 ℃.

Optionally, the volume ratio of the ethylenediamine to the water is 0.1-0.3.

Optionally, the pure silicon molecular sieve preparation raw material in the step (1) comprises: a template agent and a silicon source;

the template comprises tetrapropylammonium hydroxide and tetraethylammonium hydroxide;

the silicon source comprises at least one of tetraethoxysilane, white carbon black, silica sol and sodium silicate.

Optionally, SiO in the silica sol₂The content was 40 wt%.

Optionally, the molar ratio of each substance in the mixture in the step (1) satisfies:

template agent: 0.25-1.0% of silicon source: 1;

metal complexes: SiO 2₂＝0.00225～0.0225：1；

H₂O：SiO₂＝30～60：1；

Wherein the mole number of the silicon source is SiO₂In terms of moles;

the number of moles of the template is calculated by the number of moles of the template itself;

the number of moles of the metal complex is based on the number of moles of the metal element.

Alternatively, the metal complex is present in a molar amount of [ M (NH)₂CH₂CH₂NH₂)₂]²⁺And (4) calculating.

Optionally, the mixture of step (1) is obtained by:

(S1) obtaining a solution containing a templating agent, i.e., solution I;

(S2) adding the metal source solution into the solution I, and stirring to obtain a solution II;

(S3) adding a silicon source to the solution II, and stirring to obtain the mixture.

Optionally, in the step (S2), the metal source is a metal complex, and the metal source solution is a solution in the process of preparing the metal source; specifically, the method comprises the following steps: adding metal salt into a mixed solution of ethylenediamine and water, and stirring for 1-5 hours at 25-80 ℃ to obtain metal [ M (NH)₂CH₂CH₂NH₂)₂]²⁺(M is Pt or Zn) complex solution.

Optionally, the metal salt is selected from soluble salts of metals.

Optionally, the metal salt is selected from at least one of a chloride of the metal, a nitrate of the metal, a sulfate of the metal, and an acetate of the metal.

Optionally, the metal salt is a zinc salt or a platinum salt; the zinc salt is selected from zinc acetate, zinc chloride, zinc nitrate or zinc sulfate; the platinum salt is selected from platinum chloride, chloroplatinic acid, ammonium chloroplatinate or sodium chloroplatinate.

As a specific embodiment, the mixture in step (1) is obtained by a method comprising:

1) diluting a tetrapropylammonium hydroxide or tetraethylammonium hydroxide template agent aqueous solution in water, and stirring at 25-60 ℃ for 0.5-2 hours to obtain a uniform solution;

2) adding metal salt into a mixed solution of ethylenediamine and water, and stirring for 1-5 hours at 25-80 ℃ to obtain metal [ M (NH)₂CH₂CH₂NH₂)₂]²⁺(M is Pt or Zn) complex solution;

3) adding the complex solution obtained in the step 2) into the solution obtained in the step 1), and stirring for 1-5 hours at 25-60 ℃;

4) and adding a silicon source into the solution, and stirring for 1-8 hours at 25-60 ℃ to obtain a uniform mixture.

Optionally, in the process of obtaining the mixture in step (1), the feeding sequence of each raw material can be adjusted according to requirements.

Optionally, the hydrothermal crystallization conditions in step (1) are:

crystallizing at 80-170 ℃ for 8-72 hours.

Optionally, the upper temperature limit of the hydrothermal crystallization is selected from 120 ℃, 160 ℃ or 170 ℃; the lower limit is selected from 80 ℃, 120 ℃ or 160 ℃.

Optionally, the upper limit of the hydrothermal crystallization time is selected from 48 hours or 72 hours; the lower limit is selected from 8 hours or 48 hours.

Optionally, the volume concentration of hydrogen in the hydrogen-containing atmosphere in the step (2) is 40-100%.

Optionally, the upper limit of the volume concentration of hydrogen in the hydrogen-containing atmosphere is selected from 60%, 80%, or 100%; the lower limit is selected from 40%, 60% or 80%.

Optionally, the hydrogen-containing atmosphere is a hydrogen/nitrogen mixture, a hydrogen/argon mixture, or a hydrogen/helium mixture.

Alternatively, step (2) does not include a calcination step and is directly subjected to hydrogen reduction.

Optionally, the heating reduction conditions in step (2) are as follows:

the gas flow is 30 ml/min-80 ml/min;

the reduction temperature is 300-500 ℃;

the reduction time is 1-4 hours.

Optionally, the upper gas flow limit is selected from 50ml/min, 60ml/min or 80 ml/min; the lower limit is selected from 30ml/min, 50ml/min or 60 ml/min.

Optionally, the upper reduction temperature limit is selected from 350 ℃, 400 ℃, 450 ℃ or 500 ℃; the lower limit is selected from 300 deg.C, 350 deg.C, 400 deg.C or 450 deg.C.

Alternatively, the upper reduction time limit is selected from 2 hours, 3 hours, or 4 hours; the lower limit is selected from 1 hour, 2 hours, or 3 hours.

Optionally, the reduction is in a tube furnace.

As a specific embodiment, the reducing conditions include: the inner diameter of the quartz tube of the reduction tube furnace device is 10mm, and the height of the filler is 10 mm-30 mm.

As a specific embodiment, the preparation method of the catalyst comprises the following steps:

(1) the synthesis of the catalyst adopts tetrapropylammonium hydroxide (TPAOH) or tetraethylammonium hydroxide (TEAOH) as a template agent and noble metal [ M (NH)₂CH₂CH₂NH₂)₂]Cl₂The (M is Pt or Zn) complex is used as a precursor, and is synthesized under the traditional hydrothermal condition, and the preparation steps are as follows:

a1) diluting 25% tetrapropylammonium hydroxide template agent water solution in water, and stirring for 0.5-2 hours at 25-60 ℃ to obtain a uniform solution;

a2) adding metal salt into a mixed solution of ethylenediamine and water, and stirring for 1-5 hours at 25-80 ℃ to obtain metal [ M (NH)₂CH₂CH₂NH₂)₂]²⁺(M is Pt or Zn) complex solution;

a3) adding the complex solution obtained in the step a2) into the solution obtained in the step 1), and stirring for 1-5 hours at 25-60 ℃;

a4) adding a silicon source into the solution, and stirring for 1-8 hours at 25-60 ℃ to obtain a uniform mixture;

a5) transferring the solution obtained in the step a4) to a stainless steel reaction kettle, and then placing the reaction kettle into an oven for constant-temperature crystallization, wherein the crystallization temperature is 80-170 ℃, and the crystallization time is 8-72 hours; after crystallization is finished, taking out the reaction kettle, naturally cooling to room temperature, centrifuging substances in the reaction kettle to separate out a solid product, repeatedly washing the solid product to be neutral by using deionized water, and drying in an oven at 60-90 ℃ to obtain Metal @ S-1 molecular sieve raw powder;

a6) heating and reducing Metal @ Silicalite-1 molecular sieve raw powder obtained in the step a5) under the blowing of a hydrogen/nitrogen mixed gas to obtain Pt @ S-1-H and PtZn @ S-1-H catalysts.

In the above step, the molar ratio of each substance in the initial solution mixture is template: SiO 2₂＝0.25～1.0：1，[M(NH₂CH₂CH₂NH₂)₂]²⁺：SiO₂＝0.00225～0.0225：1，H₂O：SiO₂＝30～60: 1; silicon source is SiO as effective component₂Counting;

the mass fraction of the template agent in the tetrapropylammonium hydroxide or tetraethylammonium hydroxide template agent aqueous solution is 25%.

The silicon source is ethyl silicate, white carbon black and silica Sol (SiO)₂40 wt%) or sodium silicate.

The platinum salt is platinum chloride, platinum acetate, chloroplatinic acid or platinum nitrate.

The zinc salt is zinc acetate, zinc chloride, ammonium chloroplatinate or sodium chloroplatinate.

The inner diameter of the quartz tube of the reduction tube furnace device adopted in the step a6) is 10mm, and the height of the filler is 10 mm-30 mm; the concentration of the hydrogen/nitrogen mixed gas is 40-100%, and the gas flow is 30-80 ml/min; the reduction temperature is 300-500 ℃, and the reduction time is 1-4 hours.

In yet another aspect of the present application, there is provided a method for propane dehydrogenation, comprising: carrying out contact reaction on a gas containing propane and a catalyst to carry out propane dehydrogenation;

wherein the catalyst is at least one selected from the group consisting of the catalyst according to any one of the above and the catalyst obtained by the production method according to any one of the above.

Optionally, the volume content of propane in the propane-containing gas is 25% to 100%;

the flow rate of the gas is 40 ml/min-100 ml/min.

Optionally, the upper limit of the volume content of propane in the propane-containing gas is selected from 50%, 75% or 100%; the lower limit is selected from 25%, 50% or 75%.

Optionally, the upper flow limit of the gas is selected from 60ml/min, 80ml/min or 100 ml/min; the lower limit is selected from 40ml/min, 60ml/min, or 80 ml/min.

Optionally, the propane-containing gas comprises nitrogen.

Optionally, the propane-containing gas is a mixture of propane and nitrogen.

Optionally, hydrogen is included in the propane-containing gas.

Optionally, the propane-containing gas comprises propane, nitrogen, and hydrogen.

Optionally, the reaction conditions are:

the reaction temperature is 500-600 ℃;

the reaction pressure is 0.1-0.2 MPa.

Optionally, the upper reaction temperature limit is selected from 520 ℃, 550 ℃, 580 ℃, or 600 ℃; the lower limit is selected from 500 deg.C, 520 deg.C, 550 deg.C or 580 deg.C.

Alternatively, the upper reaction pressure limit is selected from 0.12MPa, 0.15MPa, 0.18MPa, 0.2 MPa; the lower limit is selected from 0.1MPa, 0.12MPa, 0.15MPa or 0.18 MPa.

As a specific embodiment thereof, the propane dehydrogenation process comprises:

the propane dehydrogenation reaction of the catalyst is carried out in a quartz tube fixed bed reactor with the inner diameter of 20 mm under the reaction pressure of 0.1-0.2 MPa. Before dehydrogenation, mixing a catalyst (25-40 meshes) with 1g of quartz sand, and carrying out reaction at 10-30 ml/min of H under the condition of reaction temperature₂Reducing for 0.5-2 h under the flow, and then adding propane/nitrogen mixed gas. The analysis of the propane dehydrogenation reaction is carried out by adopting an Agilent 6890N gas chromatograph which is provided with a Flame Ionization Detector (FID), wherein the dosage of a catalyst is 0.025-0.3 g, the reaction temperature is 500-600 ℃, the concentration of a reactant propane in the mixed gas is 25-100%, and the gas flow is 40-100 ml/min.

The Pt @ S-1-H catalyst synthesized by the method shows excellent catalytic activity and catalytic life in the propane dehydrogenation reaction, the conversion rate of propane is still kept above 30% after the reaction is carried out for 20 hours at 550 ℃, and the selectivity of propylene is up to above 90%; while the conversion of the comparative Pt @ S-1-C and Pt/S-1-im catalysts decreased to 2% after 5.5h and 2.5h, respectively. At the same time, using monodisperse Zn²⁺After the ion-stabilized sub-nanometer Pt cluster (the average Pt atom number is 3), the catalytic stability of PtZn @ S-1-H is further improved, the conversion rate of propane is still kept above 40% after 200H of reaction, and meanwhile, the selectivity of propylene is improved to above 99%.

The application develops a method for directly reducing hydrogen, and removes a template agent and a ligand while reducing metal; the method saves the cost of the calcining process, simultaneously avoids the agglomeration of metal in the calcining process, successfully encapsulates the sub-nano platinum clusters with only 1-10 platinum atoms and the monodisperse Zn (II) into the pure silicon molecular sieve (Silicalite-1 and the like) for the first time, and realizes the atomic-scale dispersion of the metal on the molecular sieve carrier. Because the single-site Zn (II) stable sub-nano platinum cluster is used instead of the traditional PtZn alloy and is introduced into the propane dehydrogenation reaction, the catalytic performance and the catalytic stability of the catalyst are greatly and obviously improved.

According to the method, the pure silicon molecular sieve Silicalite-1 is used for successfully packaging the sub-nano Pt cluster (the number of Pt atoms in the cluster is 1-10, the average number of Pt atoms is 3) by a hydrogen direct reduction method, the agglomeration of the sub-nano Pt cluster is limited by a molecular sieve microporous pore channel, the atomic-level dispersion of metal is realized, and the thermal stability of the Pt metal cluster in propane dehydrogenation is greatly improved. Further, on the basis, after the Zn element is introduced, the propylene selectivity and the catalytic stability of the Pt @ S-1 catalyst in the propane dehydrogenation reaction are greatly improved by using a mode of stabilizing the sub-nano platinum cluster by using single-site Zn (II) instead of forming a PtZn alloy.

The application introduces the single-site Zn (II) stable sub-nanometer Pt cluster (the average Pt atom number is 3) into the propane dehydrogenation reaction for the first time, but not the traditional catalyst of PtZn alloy, so that the catalytic efficiency and stability of the platinum cluster are greatly and obviously improved, the conversion rate at 550 ℃ reaches more than 40 percent under the catalytic condition without introducing extra hydrogen, and the selectivity of propylene can reach 99.3 percent. No obvious deactivation was observed during the on-line reaction for more than 200 h. The catalytic performance is greatly higher than that of other platinum-based catalysts reported so far, and the catalyst has great application prospect in practical industrial application.

In the application, the term "single site" means that a single + 2-valent Zn ion is connected with a silicon atom on a molecular sieve framework through a bridging oxygen atom and is stabilized in the molecular sieve framework or pore channel, and the Zn ion at the single site does not have a Zn-Zn bond of the traditional Zn nano particle and a Zn-O-Zn bond in the zinc oxide nano particle. The structural characteristics of the unit points determine that the unit points can be stably fixed in the framework or pore channels of the molecular sieve material under the high-temperature condition, and the unit points and the sub-nanometer platinum clusters in the pore channel limitation of the molecular sieve form a synergistic effect to improve the catalytic propane dehydrogenation performance.

The beneficial effects that this application can produce include:

1) the catalyst provided by the application has the advantages that the sub-nanometer platinum cluster (the average Pt atom number is 3) consisting of only 1-10 platinum atoms is packaged on the pure silicon molecular sieve, and the excellent catalytic activity and the catalytic life are shown in the propane dehydrogenation reaction.

2) The method for directly reducing hydrogen provided by the application obviously improves the agglomeration of metal in the traditional air calcination process, and successfully synthesizes the Pt @ pure silicon molecular sieve catalyst in which the sub-nano platinum cluster (the average Pt atom number of the cluster is 3) with only 1-10 platinum atoms is encapsulated in a molecular sieve; the metal size of the Pt @ S-1-C catalyst synthesized by the calcination reduction method is 3.1 nm; the Pt/S-1-im catalyst synthesized by the traditional impregnation method is more up to 6.4 nm. Meanwhile, in the PtZn @ S-1-H catalyst synthesized after introduction of Zn, the size of the platinum cluster does not increase. In addition, compared with the traditional calcining-reducing process, the direct hydrogen reduction method is simpler, saves energy, reduces consumption and reduces time cost.

Drawings

FIG. 1 is a STEM photograph of (A, B) Pt @ S-1-H catalyst of example 1; TEM photographs and particle size distributions of (C, D) Pt @ S-1-C and (E, F) Pt/S-1-im catalysts;

FIG. 2 is an XRD pattern of the catalyst prepared in example 1;

FIG. 3 is a STEM photograph of PtZn4@ S-1-H catalyst, where (I-K, M, N) is HAADF mode and the white bright spots within the circles in (M, N) are sub-nanometer Pt clusters; FIG. L is an ABF mode picture, the lower right part of which is a molecular sieve structure fitted by software;

FIG. 4 is a graph of the catalytic performance of PDH reactions over different catalysts in example 2; wherein FIG. 4A is the conversion of propane over various catalysts; FIG. 4B is propylene selectivity over various catalysts; FIG. 4C shows the long term stability test results for PDH conversion over PtZn4@ S-1-H and Pt @ S-1-H catalysts.

FIG. 5 is an XRD spectrum (A) and a TEM electron micrograph (B-D) of PtZn4@ Beta-H catalyst in example 6, and FIG. B is a TEM electron micrograph of the catalyst at a low magnification; fig. C, D are the results after 15 seconds and 30 seconds of TEM electron beam irradiation.

Detailed Description

The present application will be described in detail with reference to examples, but the present application is not limited to these examples.

Unless otherwise specified, the raw materials in the examples of the present application were all purchased commercially, and tetraethyl orthosilicate (TEOS), silica, sodium silicate nonahydrate, and ethylenediamine (NH) were used₂CH₂CH₂NH₂) Chloroplatinic acid hexahydrate, tetrapropylammonium hydroxide solution (TPAOH, 25% by weight) and tetraethylammonium hydroxide solution (TEAOH, 25% by weight) were purchased from pharmaceutical chemicals, Inc., platinum dichloride (PtCl)₂) Zinc nitrate hexahydrate, zinc chloride purchased from Aladdin reagent Ltd, silica Sol (SiO)₂40 wt%), ammonium chloroplatinate, sodium chloroplatinate hexahydrate, zinc acetate dihydrate, zinc sulfate heptahydrate, from sejin guanfu chemicals, inc, deionized water from Milli-Q bulk water purification systems (Millipore, 18.2M Ω cm-1).

In the embodiment, the source of Pt @ S-1-C is 1g of Pt @ S-1 molecular sieve raw powder synthesized in the step 5) in the embodiment 1, the temperature is raised to 550 ℃ in the air for 6 hours, and the template agent is removed by heat preservation and calcination at 550 ℃ for 6 hours; then, the temperature was raised to 400 ℃ for 2 hours in an atmosphere of 10% hydrogen gas flow rate of 60ml/min, and then maintained at 400 ℃ for 2 hours.

The source of Pt/S-1-im was synthesized by means of equivalent impregnation. First, 1g of Silicalite-1 molecular sieves (J.Am.chem.Soc.2016,138,7484-7487) calcined to remove the template agent was added with stirring 0.2ml of 0.193M H previously prepared₂PtC₆The solution was stirred at 40 ℃ for 1 hour and then dried at 80 ℃ for 6 hours. Finally, in the atmosphere with 10 percent of hydrogen gas flow rate of 60ml/min, the temperature is raised to 400 ℃ for 2 hours, and then the Pt/S-1-im catalyst can be obtained after the reduction is kept at 400 ℃ for 2 hours.

In the examples, S-1 represents Silicalite-1 molecular sieves.

The analysis method in the examples of the present application is as follows:

STEM analysis was performed using a Japanese Electron JEM-ARM300F electron microscope.

Use of a Nippon Rigaku D-Max 2550 diffractometer on a Cu target

XRD analysis was performed under the conditions.

The EXAFS data analysis was performed in fluorescence mode using BL14W1 and BL15U1 rays from Shanghai synchrotron radiation light sources.

The conversion, selectivity, in the examples of the present application were calculated as follows:

in the examples of the present application, the propane conversion and propylene selectivity were calculated by:

conversion rate

Selectivity is

Wherein, [ CH ]₄]、[C₂H₄]、[C₂H₆]、[C₃H₆]、[C₃H₈]Are respectively CH in the product₄、C₂H₄、C₂H₆、C₃H₆、C₃H₈The concentration of (c).

Example 1

The synthetic proportion of the PtZnx @ S-1-H (x ═ 0-4) catalyst is SiO₂:TPAOH:H₂O:A([Pt(NH₂CH₂CH₂NH₂)₂]Cl₂):B([Zn(NH₂CH₂CH₂NH₂)₃](OAc)₂)＝1:0.4:35:A:B(A＝2.25×10^-3a/B-1/1, 1/2, 1/3, 1/4, with no B added and with no a added), the specific synthetic steps are as follows:

1) mixing 13g of TPAOH solution with 15g of deionized water, and stirring for 1 hour at 25 ℃ for dilution;

2) 0.024g of PtCl₂Adding into 0.15ml mixed solution of ethylenediamine and water (the volume ratio of ethylenediamine and water is 0.15:1), stirring at 60 deg.C for 1 hr to PtCl₂After complete dissolution, [ Pt (NH) is obtained₂CH₂CH₂NH₂)₂]Cl₂A solution; 0.02g, 0.039g, 0.059g, 0.078g of zinc acetate dihydrate (corresponding to Pt/Zn molar ratios of 1/1, 1/2, 1/3 and 1/4, respectively) was added to 0.3ml of a mixed solution of ethylenediamine and water (the volume ratio of ethylenediamine to water was 0.3:1), and after stirring at 25 ℃ for 1 hour, [ Zn (NH) was obtained₂CH₂CH₂NH₂)₂](OAc)₂And (3) solution.

3) Adding the complex solution obtained in the step 2) into the solution obtained in the step 1) respectively, and then continuing stirring at 25 ℃ for 1 h;

4) 8.32g TEOS was added and stirred at 25 deg.C for 8 hours to obtain a homogeneous mixture after complete hydrolysis of TEOS.

5) Transferring the solution obtained in the step 4) into a stainless steel reaction kettle, and then putting the reaction kettle into an oven to perform constant temperature crystallization at 170 ℃ for 72 hours; after crystallization is finished, taking out the reaction kettle, naturally cooling to room temperature, centrifuging substances in the reaction kettle to separate out a solid product, repeatedly washing the solid product to be neutral by using deionized water, and drying in an oven at 80 ℃ to obtain PtZnx @ S-1 molecular sieve raw powder;

6) 1g of the PtZnx @ S-1 molecular sieve raw powder obtained in the step 5) is heated to 400 ℃ for 2 hours in an atmosphere with 100% hydrogen gas flow rate of 60ml/min, and then is kept at 400 ℃ for 2 hours to obtain a PtZnx @ S-1-H catalyst (the supported amount of Pt in the PtZn4@ S-1-H catalyst is 0.75 wt%); respectively Pt @ S-1-H catalyst, PtZn2@ S-1-H catalyst, PtZn3@ S-1-H catalyst, PtZn4@ S-1-H catalyst and Zn4@ S-1-H catalyst.

The XRD pattern of the PtZnx @ S-1-H catalyst is shown in figure 2, and it can be seen that the catalyst prepared in example 1 has an intact MFI topology.

STEM electron micrographs of PtZn4@ S-1-H catalyst are shown in FIG. 3, with (I-K, M, N) being STEM-HAADF mode; it can be seen from the figure that the size of the metal in the catalyst prepared in example 1 is less than 0.6 nm; while the EXAFS results in Table 1 demonstrate that the coordination number of Pt-Pt is about 2, indicating that the Pt cluster is composed of 3 Pt atoms on average, while the absence of Zn-Zn coordination indicates that Zn is single-site Zn (II) dispersed on the molecular sieve, and the presence of Zn-O bonds (coordination number of 3) demonstrates that Zn is connected to Si atoms on the framework via oxygen atoms to form a single-site structure.

TABLE 1 EXAFS data for PtZn4@ S-1-H, Pt @ S-1-H and Pt @ S-1-C catalysts

Wherein FIG. 1 is a STEM photograph of (A, B) Pt @ S-1-H catalyst; TEM photographs and particle size distributions of (C, D) Pt @ S-1-C and (E, F) Pt/S-1-im catalysts; as can be seen from the figure, the Pt/S-1-im prepared by the common impregnation method has the largest metal particle size and the average particle size of 6.4nm, and is distributed on the surface of the molecular sieve crystal; the metal nano particles of Pt @ S-1-C are encapsulated in the molecular sieve, and the average particle size is only 3.1 nm; the Pt @ S-1-H reduced by direct hydrogen has the smallest Pt metal size and is encapsulated in the microporous pore canal (less than 1nm) of the molecular sieve. This also demonstrates the great advantage of the direct hydrogen reduction method over the traditional methods in preparing ultra-small metal particles.

The STEM and EXAFS results for the other catalysts in example 1 were similar to those for the PtZn4@ S-1-H catalyst described above: the other catalysts of example 1 have Pt clusters consisting of an average of 3 Pt atoms, Zn being single site Zn (ii) dispersed on the molecular sieve.

Example 2

The propane dehydrogenation reaction of the catalyst is carried out in a quartz tube fixed bed reactor with the inner diameter of 20 mm under the reaction pressure of 0.1 MPa. Before dehydrogenation, 0.3g of catalyst was addedMixing the reagent (25-40 mesh) with 1g of quartz sand, and reacting at 550 ℃ under the condition of 10ml/min of H₂Reducing for 1h under flowing, adding propane/nitrogen mixed gas with the volume fraction of 25% of propane to react, wherein the flow rate of the mixed gas is 40ml/min (C)₃H₈/N₂＝10/30ml min^-1). Wherein the PtZnx @ S-1-H catalyst was the catalyst prepared in example 1.

The propane dehydrogenation catalytic reaction in fig. 4 demonstrates that fig. 4A is the conversion of propane over various catalysts; FIG. 4B is propylene selectivity over various catalysts; FIG. 4C shows the long term stability test results for PDH conversion over PtZn4@ S-1-H and Pt @ S-1-H catalysts. It can be seen from the graph that Pt @ S-1-H has a higher initial propane conversion (54.1%) than Pt @ S-1-C (38.0%) and Pt/S-1-im (24.4%) catalysts. After 20 hours, the propane conversion dropped to 34.2% with a propylene selectivity of 95.4%. In contrast, the propane conversion for the Pt @ S-1-C and Pt/S-1-im catalysts dropped rapidly to 2% over 340 and 160 minutes, respectively. The improved catalytic activity of Pt @ S-1-H over Pt @ S-1-C and Pt/S-1-im is due primarily to the significant reduction in platinum size and the greater number of active sites for propane conversion. The initial propylene selectivity for the propane dehydrogenation reaction was 79.0%.

Introduction of single point Zn²⁺And the selectivity and the catalytic stability of the propylene can be obviously improved by combining with the sub-nano platinum cluster compound. As the zinc content increased, the initial propylene selectivity increased, reaching 93.2% for PtZn4@ S-1-H, which is much higher than Pt @ S-1-H (79.0%). The PtZn4@ S-1-H catalyst maintained a higher propane conversion (44.8%) and a higher propylene selectivity (98.9%) after 20 hours. It is noteworthy that at 216.7 hours (WHSV ═ 3.6 h)^-1) Thereafter, the propane conversion was maintained at 40.4% and the propylene selectivity was 99.2%. In contrast, the propane conversion of Pt @ S-1-H dropped sharply to 19.8% after 48.3 hours. The result shows that the bimetal PtZn4@ S-1-H has extremely high long-term stability which is far superior to the monomer Pt @ S-1-H. Meanwhile, the catalyst PtZn4@ S-1-H lasts for 3.6H^-1The conversion rate of more than 40 percent is still maintained after 216.7 hours, and the deactivation rate constant k_dIs only 0.001h^-1Loss of bloodThe activity speed is far lower than that of other Pt-based catalysts, and the catalyst has the most excellent catalytic stability for propane dehydrogenation (see Table 2).

Meanwhile, 0.025g of PtZn4@ S-1-H catalyst (25-40 mesh) was mixed with 1.275g of quartz sand at a reaction temperature of 550 ℃ in 10ml/min of H₂Reducing for 0.5h under flowing, adding propane/nitrogen mixed gas with 25% propane volume fraction, reacting under 0.1MPa, the flow rate of the mixed gas is 100ml/min (C)₃H₈/N₂＝25/75ml min^-1) PtZn4@ S-1-H catalyst at WHSV of 108H^-1The propylene production activity of the catalyst reaches 3.55mol_C3H6mol_Pt ^-1s^-1TOF value of 65.5mol_C3H6g_Pt ^-1h^-1. The TOF value represents the highest catalytic activity for the dehydrogenation of propane to propylene, much higher than that of the other reported platinum-based catalysts (see table 2). (the same procedure as in example 2 was followed except that the parameters in Table 2 were used in the dehydrogenation of propane)

TABLE 2 comparison of propane dehydrogenation Performance of Pt-based catalysts

(a) Reactivity is the moles of propylene produced per mole of Pt per second

(b) Rate constant of deactivation

Con_FinalAnd Con_InitialIs the final and initial propane conversion, and t is the time of reaction in hours.

Wherein, the citations in table 2 are:

1.X.Q.Fan,J.M.Li,Z.Zhao,Y.C.Wei,J.Liu,A.J.Duan,G.Y.Jiang,Dehydrogenation of propane over PtSnAl/SBA-15catalysts:Al addition effect and coke formation analysis.Catal.Sci.Tech.5,339-350(2015)

2.T.Otroshchenko,S.Sokolov,M.Stoyanova,V.A.Kondratenko,U.Rodemerck,D.Linke,E.V.Kondratenko,ZrO₂-based alternatives to conventional propane dehydrogenation catalysts:active sites,design,and performance.Angew.Chem.Int.Ed.54,15880-15883(2015)

3.O.A.Barias,A.Holmen,E.A.Blekkan,Propane dehydrogenation over supported Pt and Pt-Sn catalysts:catalyst preparation,characterization,and activity measurements.J.Catal.158,1-12(1996)

4.L.D.Deng,H.Miura,T.Shishido,S.Hosokawa,K.Teramura,T.Tanaka,Strong metal-support interaction between Pt and SiO₂following high-temperature reduction:a catalytic interface for propane dehydrogenation.Chem.Commun.53,6937-6940(2017)

5.B.Li,Z.X.Xu,F.L.Jing,S.Z.Luo,W.Chu,Facile one-pot synthesized ordered mesoporous Mg-SBA-15supported PtSn catalysts for propane dehydrogenation.Appl.Catal.A-Gen.533,17-27(2017)

6.J.Liu,Y.Y.Yue,H.Y.Liu,Z.J.Da,C.C.Liu,A.Z.Ma,J.F.Rong,D.S.Su,X.J.Bao,H.D.Zheng,Origin of the Robust Catalytic Performance of nanodiamond graphene-supported Pt nanoparticles used in the propane dehydrogenation reaction.ACS Catal.7,3349-3355(2017)

7.H.F.Xiong,S.Lin,J.Goetze,P.Pletcher,H.Guo,L.Kovarik,K.Artyushkova,B.M.Weckhuysen,A.K.Datye,Thermally stable and regenerable platinum-tin clusters for propane dehydrogenation prepared by atom trapping on ceria.Angew.Chem.Int.Ed.56,8986-8991(2017)

8.Y.Xu,J.N.Chen,X.L.Yuan,Y.Zhang,J.Q.Yu,H.Y.Liu,M.H.Cao,X.Fan,H.P.Lin,Q.Zhang,Sintering-resistant Pt on Ga₂O₃rods for propane dehydrogenation:the morphology matters.Ind.Eng.Chem.Res.57,13087-13093(2018)

9.E.A.Redekop,V.V.Galvita,H.Poelman,V.Bliznuk,C.Detavernier,G.B.Marin,Delivering a Modifying Element to Metal Nanoparticles via Support:Pt-Ga alloying during the reduction of Pt/Mg(Al,Ga)O-x catalysts and its effects on propane dehydrogenation.ACS Catal.4,1812-1824(2014)

example 3

In addition, the proportion of the PtZn4@ S-1-H catalyst synthesized by adopting other raw materials is SiO₂:TPAOH:H₂O:([Pt(NH₂CH₂CH₂NH₂)₂]²⁺):([Zn(NH₂CH₂CH₂NH₂)₃](NO₃)₂)＝1:0.25:30:4.5×10^-3:1.8×10^-2The specific synthesis steps are as follows:

1) mixing 8.1g of TPAOH solution with 13g of deionized water, and stirring at 60 ℃ for 0.5 hour to dilute;

2) 0.093g of chloroplatinic acid hexahydrate was added to 0.3ml of a mixed solution of ethylenediamine and water (the volume ratio of ethylenediamine to water was 0.15:1), and the mixture was stirred at 25 ℃ for 5 hours to obtain [ Pt (NH)₂CH₂CH₂NH₂)₂]²⁺A solution; 0.21g of zinc nitrate hexahydrate was added to 0.6ml of a mixed solution of ethylenediamine and water (the volume ratio of ethylenediamine to water was 0.3:1), and the mixture was stirred at 60 ℃ for 1 hour to obtain [ Zn (NH)₂CH₂CH₂NH₂)₂](NO₃)₂And (3) solution.

3) Adding the complex solution obtained in the step 2) into the solution obtained in the step 1) respectively, and then continuously stirring and stirring for 1h at the temperature of 60 ℃;

4) 2.4g of white carbon black was added and stirred at 60 ℃ for 1 hour to obtain a uniform mixture.

5) Transferring the solution obtained in the step 4) into a stainless steel reaction kettle, and then putting the reaction kettle into an oven to perform constant temperature crystallization for 8 hours at 160 ℃; taking out the reaction kettle after crystallization is finished, naturally cooling to room temperature, centrifuging substances in the reaction kettle to separate a solid product, repeatedly washing the solid product to be neutral by using deionized water, and drying in a 90 ℃ oven to obtain PtZn4@ S-1 molecular sieve raw powder;

6) and (3) heating 0.5g of the PtZn4@ S-1 molecular sieve raw powder obtained in the step 5) for 2 hours in an atmosphere (a mixed gas of hydrogen and argon) with a volume fraction of 40% and a hydrogen gas flow rate of 80ml/min, and then keeping the temperature at 500 ℃ for 4 hours to obtain the PtZn4@ S-1-H catalyst (the loading amount of Pt is 0.95 wt%).

The synthesized PtZn4@ S-1-H catalyst was also subjected to a propane dehydrogenation reaction test in a quartz tube fixed bed reactor having an inner diameter of 20 mm at a reaction pressure of 0.2 MPa. Before dehydrogenation, 0.3g of catalyst (25-40 mesh) was mixed with 1g of quartz sand at 600 ℃ in 30ml/min of H₂Reducing for 0.5 hour under flowing down, adding propane/nitrogen mixed gas with propane volume fraction of 50% for reaction, wherein the flow rate of the mixed gas is 80ml/min (C)₃H₈/N₂＝40/40ml min^-1)。

Under the reaction condition, the initial propane conversion rate of PtZn4@ S-1-H is as high as 66.7%, and the propylene selectivity can reach over 90%. Higher propane conversion (43.2%) and propylene selectivity (over 95%) were maintained after 58 hours on-line reaction. The result shows that the bimetallic PtZn4@ S-1-H still has higher stability and keeps extremely high propylene selectivity under the high-temperature reaction condition.

Example 4

In addition, the proportion of the PtZn4@ S-1-H catalyst synthesized by adopting other raw materials is SiO₂:TPAOH:H₂O:([Pt(NH₂CH₂CH₂NH₂)₂]²⁺):([Zn(NH₂CH₂CH₂NH₂)₃]Cl₂)＝1:0.8:35:1.5×10^-3:6×10^-3The specific synthesis steps are as follows:

1) mixing 26g of TPAOH solution with 5.25g of deionized water, and stirring for 2 hours at 40 ℃ for dilution;

2) 0.027g of ammonium chloroplatinate was added to 0.1ml of a mixed solution of ethylenediamine and water (the volume ratio of ethylenediamine to water was 0.1:1), and after stirring at 80 ℃ for 1 hour, [ Pt (NH) ] was obtained₂CH₂CH₂NH₂)₂]²⁺A solution; 0.033g of zinc chloride (corresponding to a Pt/Zn molar ratio of 1/4) was added to 0.2ml of a mixed solution of ethylenediamine and water (the volume ratio of ethylenediamine to water was 0.2:1)Stirring at 40 deg.C for 2 hr to obtain [ Zn (NH)₂CH₂CH₂NH₂)₂]Cl₂And (3) solution.

3) Adding the complex solution obtained in the step 2) into the solution obtained in the step 1) respectively, and then continuously stirring and stirring for 3 hours at the temperature of 60 ℃;

4) 6g of silica Sol (SiO) was added₂ Content 40 wt%), and after stirring for 2 hours at 60 c, a homogeneous mixture was obtained.

5) Transferring the solution obtained in the step 4) into a stainless steel reaction kettle, and then putting the reaction kettle into an oven to perform constant temperature crystallization at 80 ℃ for 72 hours; taking out the reaction kettle after crystallization is finished, naturally cooling to room temperature, centrifuging substances in the reaction kettle to separate a solid product, repeatedly washing the solid product to be neutral by using deionized water, and drying in an oven at 60 ℃ to obtain PtZn4@ S-1 molecular sieve raw powder;

6) 1.5g of the PtZn4@ S-1 molecular sieve raw powder obtained in the step 5) is heated to 500 ℃ for 2 hours in an atmosphere (a mixed gas of hydrogen and nitrogen) with a volume fraction of 80% and a hydrogen gas flow rate of 50ml/min, and then is kept at 500 ℃ for 1 hour to obtain the PtZn4@ S-1-H catalyst (the loading amount of Pt is 0.55 wt%).

The propane dehydrogenation reaction of the catalyst was also carried out in a quartz tube fixed bed reactor having an inner diameter of 20 mm at a reaction pressure of 0.15 MPa. Before dehydrogenation, 0.3g of catalyst (25-40 mesh) was mixed with 1.0g of quartz sand at 520 ℃ in 20ml/min of H₂The reaction solution was reduced under a stream for 2 hours, and then 100% pure propane gas was added thereto to carry out the reaction at a gas flow rate of 40 ml/min.

The initial propylene selectivity of PtZn4@ S-1-H is as high as 97.5%, and the conversion rate of propylene is as high as more than 30%. It is noted that after 140 hours of reaction, the propane conversion remained above 28% and the propylene selectivity was 99%. The result shows that the bimetallic PtZn4@ S-1-H still has higher stability and keeps extremely high propylene selectivity under the reaction condition of pure propane atmosphere.

Example 5

In addition, PtZn4@ S-1-H catalyst is synthesized by adopting other raw materialsThe proportion of the chemical agent is SiO₂:TPAOH:H₂O:([Pt(NH₂CH₂CH₂NH₂)₂]²⁺):([Zn(NH₂CH₂CH₂NH₂)₃]Cl₂)＝1:1.0:60:2.25×10^-3:9×10^-3The specific synthesis steps are as follows:

1) mixing 32.5g of TPAOH solution with 2g of deionized water, and stirring for 1 hour at 60 ℃ for dilution;

2) 0.051g of sodium chloroplatinate hexahydrate is added into 0.15ml of mixed solution of ethylenediamine and water (the volume ratio of ethylenediamine to water is 0.15:1), and after stirring is carried out for 2 hours at 60 ℃, the [ Pt (NH) is obtained₂CH₂CH₂NH₂)₂]²⁺A solution; 0.104g of zinc sulfate heptahydrate (corresponding to a Pt/Zn molar ratio of 1/4) was added to 0.3ml of a mixed solution of ethylenediamine and water (the volume ratio of ethylenediamine to water was 0.3:1), and after stirring at 60 ℃ for 2 hours, [ Zn (NH) (I) was obtained₂CH₂CH₂NH₂)₂]SO₄And (3) solution.

4) 11.4g of sodium silicate nonahydrate were added and stirred at 60 ℃ for 3 hours to obtain a uniform mixture.

5) Transferring the solution obtained in the step 4) into a stainless steel reaction kettle, and then putting the reaction kettle into an oven for constant-temperature crystallization at 120 ℃ for 48 hours; taking out the reaction kettle after crystallization is finished, naturally cooling to room temperature, centrifuging substances in the reaction kettle to separate a solid product, repeatedly washing the solid product to be neutral by using deionized water, and drying in an oven at 80 ℃ to obtain PtZn4@ S-1 molecular sieve raw powder;

6) and (3) heating 0.5g of the PtZn4@ S-1 molecular sieve raw powder obtained in the step 5) for 2 hours in an atmosphere (a mixed gas of hydrogen and helium) with a volume fraction of 60% and a hydrogen gas flow rate of 30ml/min to 500 ℃, and then keeping the temperature at 500 ℃ for 3 hours to obtain the PtZn4@ S-1-H catalyst (the loading amount of Pt is 0.75 wt%).

The propane dehydrogenation reaction of the catalyst is alsoIn a quartz tube fixed bed reactor with an internal diameter of 20 mm, at a reaction pressure of 0.18 MPa. Before dehydrogenation, 0.3g of catalyst (25-40 mesh) was mixed with 1.0g of quartz sand at 500 ℃ in 30ml/min of H₂Reducing for 2 hours under the flow, then adding propane/nitrogen mixed gas with the volume fraction of propane of 75 percent to react, wherein the flow rate of the mixed gas is 60ml/min (C)₃H₈/N₂＝40/20ml min^-1)。

The initial propylene selectivity of PtZn4@ S-1-H is as high as more than 98%, and the conversion rate of propylene is as high as more than 22%. After 200 hours of continuous reaction, the propane conversion was maintained at 21% or more and the propylene selectivity was 99%. The result shows that the bimetal PtZn4@ S-1-H synthesized by the method has extremely excellent propane dehydrogenation reaction activity and can realize extremely high propylene selectivity.

The XRD patterns of PtZn4@ S-1-H catalysts in examples 3 to 5 are similar to those in fig. 2, and it can be seen that the catalysts prepared in examples 3 to 5 all retain an intact MFI topology.

Example 6

The proportion of the PtZn4@ Beta-H catalyst is SiO₂:TEAOH:H₂O:([Pt(NH₂CH₂CH₂NH₂)₂]²⁺):([Zn(NH₂CH₂CH₂NH₂)₃]Cl₂)＝1:0.5:30:1.25×10^-3:5×10^-3The specific synthesis steps are as follows:

1) mixing 11.8g of TEAOH solution with 5.25g of deionized water, and stirring at 25 ℃ for 1 hour to dilute;

2) 0.013g of PtCl₂Adding into 0.1ml mixed solution of ethylenediamine and water (the volume ratio of ethylenediamine and water is 0.1:1), stirring at 60 deg.C for 1 hr to PtCl₂After complete dissolution, [ Pt (NH) is obtained₂CH₂CH₂NH₂)₂]Cl₂A solution; 0.027g of zinc chloride (corresponding to a Pt/Zn molar ratio of 1/4) was added to 0.2ml of a mixed solution of ethylenediamine and water (the volume ratio of ethylenediamine to water was 0.2:1), and stirring was carried out at 40 ℃After stirring for 2 hours, [ Zn (NH) is obtained₂CH₂CH₂NH₂)₂]Cl₂And (3) solution.

4) 6g of silica sol were added and after stirring for 2 hours at 60 ℃ a homogeneous mixture was obtained.

5) Transferring the solution obtained in the step 4) into a stainless steel reaction kettle, and then putting the reaction kettle into an oven to perform constant temperature crystallization at 120 ℃ for 72 hours; taking out the reaction kettle after crystallization is finished, naturally cooling to room temperature, centrifuging substances in the reaction kettle to separate a solid product, repeatedly washing the solid product to be neutral by using deionized water, and drying in an oven at 60 ℃ to obtain PtZn4@ Beta molecular sieve raw powder;

6) and (3) heating 0.5g of PtZn4@ Beta molecular sieve raw powder obtained in the step 5) for 2 hours at 300 ℃ in an atmosphere of 100% hydrogen and 60ml/min of gas flow, and then keeping the temperature at 300 ℃ for 3 hours to obtain the PtZn4@ Beta-H catalyst.

The XRD of the resulting PtZn4@ Beta-H catalyst is shown in fig. 5A as BEA @ -molecular sieve topology; TEM results are shown in FIGS. 5B-D (B is TEM photograph of catalyst at low magnification; C, D is results after TEM electron beam irradiation for 15 seconds and 30 seconds), Pt metal cluster also has very small size (less than 0.6nm) and is located inside the molecular sieve; the direct hydrogen reduction method is proved to be capable of packaging the ultra-small Pt nanoclusters in the pure silicon Beta molecular sieve.

EXAFS analysis of the PtZn4@ Beta-H catalyst prepared in example 6 demonstrated that Pt-Pt has a coordination number of about 2, indicating that the Pt cluster is composed of 3 Pt atoms on average, while the absence of Zn-Zn coordination indicates that Zn is a single site Zn (II) dispersed on the molecular sieve.

The propane dehydrogenation reaction of the catalyst was also carried out in a quartz tube fixed bed reactor having an inner diameter of 20 mm at a reaction pressure of 0.12 MPa. Before dehydrogenation, 0.3g of catalyst (25-40 mesh) was mixed with 1.1g of quartz sand at 580 ℃ in 30ml/min of H₂Reduced under stream for 0.5 hour, thenAdding propane/nitrogen mixed gas with a volume fraction of 25% of propane to react, wherein the flow rate of the mixed gas is 40ml/min (C)₃H₈/N₂＝10/30ml min^-1)。

The initial propylene selectivity of PtZn4@ Beta-H is as high as more than 90 percent, and the conversion rate of propylene is as high as 51.2 percent. It is noted that after 50 hours of reaction, the propane conversion remained above 30% and the propylene selectivity was 97.5%. The result shows that the direct hydrogen reduction method is also suitable for preparing the pure silicon Beta molecular sieve catalyst loaded with metal, and the bimetallic PtZn4@ Beta-H synthesized by the method also has higher propane dehydrogenation catalytic activity, thereby realizing extremely high propylene selectivity.

Although the present application has been described with reference to a few embodiments, it should be understood that various changes, substitutions and alterations can be made herein without departing from the spirit and scope of the application as defined by the appended claims.

Claims

1. A catalyst, characterized in that the catalyst comprises a support and an active component;

the carrier is a pure silicon molecular sieve;

the active element in the active component comprises Pt; wherein Pt is supported in the support in the form of sub-nano Pt clusters;

other elements are also included in the catalyst;

the other elements are non-noble metal elements;

the non-noble metal is Zn;

the non-noble metal element exists in a + 2-valent Zn ion form and is connected with Si atoms on the framework through oxygen atoms to form a single-site structure.

2. The catalyst of claim 1, wherein the pure silica molecular sieve comprises at least one of a Silicalite-1 molecular sieve and a Beta molecular sieve.

3. The catalyst of claim 1 wherein the size of the metal in the catalyst is less than 0.6 nm.

4. The catalyst according to claim 1, wherein the loading amount of the active element in the catalyst is 0.3 to 1 wt%.

5. The catalyst according to claim 4, wherein the loading amount of the active element in the catalyst is 0.35 to 0.95 wt%.

6. The catalyst according to claim 1, wherein the molar ratio of the other element to the active element is 0 to 4: 1;

wherein the molar ratio of the other element to the active element is other than 0.

7. The catalyst of claim 1, wherein the catalyst has the general formula:

PtM_x@ Q formula I

Wherein M is other elements;

x is greater than 0 and not more than 4;

q is a pure silicon molecular sieve.

8. A process for preparing a catalyst as claimed in any one of claims 1 to 7, characterized in that it comprises:

wherein the metal source is a metal complex; the metal complex comprises a metal complex of an active element and a metal complex of other elements;

the metal complex is selected from [ T (NH)₂CH₂CH₂NH₂)₂]Cl₂、[T(NH₂CH₂CH₂NH₂)₂](NO₃)₂、[T(NH₂CH₂CH₂NH₂)₂](OAc)₂、[T(NH₂CH₂CH₂NH₂)₂]SO₄At least one of;

wherein T is a metal element;

the conditions of the hydrothermal crystallization in the step (1) are as follows:

crystallizing at the constant temperature of 80-170 ℃ for 8-72 hours;

the volume concentration of the hydrogen in the hydrogen-containing atmosphere in the step (2) is 40-100%;

the heating reduction conditions in the step (2) are as follows:

the gas flow is 30 ml/min-80 ml/min;

the reduction temperature is 300-500 ℃;

the reduction time is 1-4 hours.

9. The method of claim 8, wherein the pure silicon molecular sieve preparation feedstock in step (1) comprises: a template agent and a silicon source;

10. The method according to claim 9, wherein the molar ratio of each substance in the mixture in the step (1) is satisfied:

template agent: silicon source = 0.25-1.0: 1;

metal complexes: SiO 2₂=0.00225~0.0225：1；

H₂O：SiO₂=30~60：1；

Wherein the mole number of the silicon source is SiO₂In terms of moles;

11. A process for the dehydrogenation of propane, the process comprising: carrying out contact reaction on a gas containing propane and a catalyst to carry out propane dehydrogenation;

wherein the catalyst is selected from at least one of the catalyst of any one of claims 1 to 7, the catalyst obtained by the method of any one of claims 8 to 10.

12. The process for the dehydrogenation of propane according to claim 11, wherein the propane-containing gas has a propane content of from 25% to 100% by volume;

the flow rate of the gas is 40 ml/min-100 ml/min.

13. The process for the dehydrogenation of propane according to claim 11, wherein the propane-containing gas comprises nitrogen.

14. The process for the dehydrogenation of propane according to claim 11, wherein the reaction conditions are:

the reaction temperature is 500-600 ℃;

the reaction pressure is 0.1-0.2 MPa.