CN110813369A - Mononuclear-tin-oxygen-enriched tetrahedral silicon tin molecular sieve supported metal catalyst and preparation method and application thereof - Google Patents

Mononuclear-tin-oxygen-enriched tetrahedral silicon tin molecular sieve supported metal catalyst and preparation method and application thereof Download PDF

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CN110813369A
CN110813369A CN201911062283.1A CN201911062283A CN110813369A CN 110813369 A CN110813369 A CN 110813369A CN 201911062283 A CN201911062283 A CN 201911062283A CN 110813369 A CN110813369 A CN 110813369A
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tin
molecular sieve
silicon
metal
catalyst
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吴鹏
马跃
关业军
蒋金刚
徐浩
李晓红
吴海虹
何鸣元
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East China Normal University
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    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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    • 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
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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
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    • 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
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    • C07C—ACYCLIC OR CARBOCYCLIC COMPOUNDS
    • C07C5/00—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms
    • C07C5/32—Preparation of hydrocarbons from hydrocarbons containing the same number of carbon atoms by dehydrogenation with formation of free hydrogen
    • C07C5/327—Formation of non-aromatic carbon-to-carbon double bonds only
    • C07C5/333—Catalytic processes
    • C07C5/3335—Catalytic processes with metals
    • C07C5/3337—Catalytic processes with metals of the platinum group
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    • B01J2229/18—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself
    • B01J2229/186—After treatment, characterised by the effect to be obtained to introduce other elements into or onto the molecular sieve itself not in framework positions
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    • C07C2529/72—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups C07C2529/08 - C07C2529/65 containing iron group metals, noble metals or copper
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Abstract

The invention discloses a silicon-tin molecular sieve supported metal catalyst rich in mononuclear tin-oxygen tetrahedrons, which comprises a carrier (silicon-tin molecular sieve rich in mononuclear tin-oxygen tetrahedrons) and metal. The invention also discloses a preparation method of the catalyst, noble metal clusters or nano particles are anchored by highly dispersed tin-oxygen tetrahedrons in a molecular sieve framework, the formed noble metal-Sn clusters or crystal grains are stably confined in the pore channels of the molecular sieve, and the noble metal-Sn clusters or crystal grains and the acid synergistic action of the residual framework four-coordinate tin controllably prepare the mononuclear tin-oxygen tetrahedral silicon-tin molecular sieve-loaded metal catalyst. The catalyst shows high activity, high selectivity and high stability when low-carbon alkane (2-4 carbons) is directly dehydrogenated to prepare olefin.

Description

Mononuclear-tin-oxygen-enriched tetrahedral silicon tin molecular sieve supported metal catalyst and preparation method and application thereof
Technical Field
The invention belongs to the field of zeolite molecular sieves and industrial catalysis, and relates to a mononuclear-tin-oxygen-enriched tetrahedral silicon tin molecular sieve supported metal catalyst, and a preparation method and application thereof.
Background
At present, most of the low-carbon alkanes produced in China are directly used as fuels, the combustion efficiency is low, and the utilization value is to be improved. Lower olefins are an important component of the chemical industry, and the demand for lower olefins is increasing, leading to an increasing interest in the dehydrogenation of lower alkanes (Angewandte Chemie International Edition,2015,54, 15880; Angewandte Chemie International Edition,2015,127,16107). The price difference between alkane and alkene is large, and people pay attention to the process for producing high value-added alkene by dehydrogenating the alkane with low price. Meanwhile, natural gas resources in China are rich, and reasonable utilization of natural gas can be realized by researching the preparation of olefin through dehydrogenation of low-carbon alkane.
To date, there are mainly the following 3 methods for producing lower olefins: naphtha cracking co-production low-carbon olefin, catalytic cracking by-product low-carbon olefin, and alkane dehydrogenation to olefin. The shortage of petroleum resources and the rising price of petroleum resources are increasing day by day, and the requirement of chemical production on propylene is difficult to meet by relying on the traditional naphtha cracking and catalytic cracking to produce the byproduct propylene. A plurality of large-scale alkane dehydrogenation olefin preparation devices are put into operation worldwide, and become another main way for producing low-carbon olefins besides naphtha cracking and catalytic cracking.
Catalysts commercially used for propane dehydrogenation can be classified into two types, one being a Cr-based catalyst and the other being a Pt-based catalyst. In practical application, although the catalytic activity of the chromium-based catalyst is better than that of the platinum-based catalyst, the requirement on the purity of the raw materials is lower, and the price is relatively low, the chromium content in the chromium-based catalyst is higher, so that the environment is seriously polluted, and the human health is harmed. In recent years, chromium-based catalysts have been relatively rarely studied and are gradually replaced by noble metal catalysts.
The direct dehydrogenation of alkanes to lower olefins is commercially viable, but requires higher reaction temperatures to achieve economically attractive yields due to their endothermic nature (Chemical Reviews,2014,114,10613; Topicsin catalysts, 2012,55, 1309). The noble metals such as Pt, Pd, Rh and the like have good capability of activating C-H bonds, have weaker capability of activating C-C bonds, and are suitable low-carbon alkane direct dehydrogenation catalysts. However, noble metals are expensive, the requirement on the purity of reaction raw materials is high, and carbon deposition and coking reactions are easy to occur in the high-temperature reaction process, so that part of active centers are covered, and the activity of the catalyst is reduced (Nanoscale,2014,6, 10000); on the other hand, metal grains are easy to sinter and grow, which reduces the metal dispersity and influences the activity and selectivity of the catalyst (Angewandte Chemie International edition,2015,54, 23994).
In the current large-scale olefin preparation process by alkane dehydrogenation, which is put into production worldwide, most of the adopted catalysts are noble metals loaded on alumina, particularly noble metals Pt. The noble metal is mainly supported by a common impregnation method, so that the metal particles are large and are unevenly distributed, the growth of the metal particles is not limited, and carbon deposit and coking and sintering of the metal particles cannot be accompanied in the high-temperature reaction process, so that the activity and the product selectivity of the catalyst are influenced. Although carbon deposits can be effectively oxidized during air regeneration, redispersion of precious metals is more difficult (ACS Catalysis,2016,6, 2257).
In conclusion, the development of a high-efficiency and stable metal catalyst for dehydrogenation of light alkane has far-reaching significance.
Disclosure of Invention
In order to overcome the defects in the prior art, the invention provides a preparation method of a mononuclear-tin-oxygen-enriched tetrahedral silicon tin molecular sieve supported metal catalyst. The method has the advantages of simple synthetic process and convenient operation, greatly improves the activity and stability of the catalyst, reduces the manufacturing cost of the catalyst, is easy to realize industrial production and application, and has excellent catalytic performance.
In order to achieve the purpose, the invention adopts the following technical scheme:
a preparation method of a mononuclear-tin-oxygen-enriched tetrahedral silicon tin molecular sieve supported metal catalyst comprises the following steps:
(1) guiding the template agent to the prepared silicon-tin molecular sieve for roasting to obtain a silicon-tin molecular sieve carrier which does not contain the template agent and is rich in mononuclear tin-oxygen tetrahedrons;
(2) loading a metal precursor on the silicon-tin molecular sieve carrier prepared in the step (1) to obtain a metal catalyst precursor; and then carrying out controlled reduction reaction on the metal catalyst precursor to obtain the mononuclear tin-oxygen-enriched tetrahedral silicon tin molecular sieve supported metal catalyst.
The method specifically comprises the following steps:
(1) guiding the template agent to the prepared silicon-tin molecular sieve, and roasting at high temperature in air atmosphere to remove the template agent and water to obtain a silicon-tin molecular sieve carrier which does not contain the template agent and is rich in mononuclear tin-oxygen tetrahedrons;
(2) loading a metal precursor on the silicon-tin molecular sieve carrier prepared in the step (1) to obtain a metal catalyst precursor; and then performing controlled reduction reaction on the prepared metal catalyst precursor in a hydrogen atmosphere containing low-carbon alkane to obtain the mononuclear stannoxy tetrahedral silicon tin molecular sieve supported metal catalyst.
The invention adds low carbon alkane into hydrogen to promote the generation of metal active center by utilizing the reaction performance of alkane carbon-hydrogen bond.
In the step (1), the silicon-tin molecular sieve is selected from one or more of Sn-BEA, Sn-MFI, Sn-MOR, Sn-MWW and the like; preferably Sn-BEA.
In the step (1), the molar ratio of silicon to tin in the silicon-tin molecular sieve carrier is (30-200): 1; preferably, 80: 1.
in the step (1), roasting is carried out for 2-12 hours at 400-600 ℃ in an air atmosphere rich in water vapor, and the heating rate is 1-2 ℃/min; preferably, the roasting is carried out for 6 hours at 550 ℃ in an air atmosphere rich in water vapor, and the temperature rising rate is 1.5 ℃/min.
In the step (1), the silicon-tin molecular sieve is preferably roasted at a low temperature in an air atmosphere to remove the template agent and water.
In the step (2), the metal precursor comprises one or two of chloroplatinic acid, ammonium chloropalladate, ammonium chlororhodate, platinum nitrate, palladium nitrate, rhodium sulfate and the like; preferably, chloroplatinic acid and platinum nitrate.
In the step (2), the mass ratio of the metal precursor to the carrier is (99-99.95): (0.05-1); preferably, 99.5: 0.5.
in the step (2), the volume ratio of the low-carbon alkane to the hydrogen is (0-10): (90-100); preferably, is (0.5-10): (90-100); further preferably, it is 5: 95.
wherein the lower alkane is alkane with 2-4 carbons; preferably, it is propane.
In the step (2), the temperature of the reduction reaction is 150-600 ℃; preferably, it is 500 ℃.
In the step (2), the time of the reduction reaction is 1-4 h; preferably, it is 2 h.
After the reduction reaction is finished, a large amount of nitrogen is needed to purge the catalyst for 1-4 h; preferably, it is 2 h.
The invention also provides the mononuclear stannic oxide-rich tetrahedral silicon tin molecular sieve supported metal catalyst prepared by the method.
Wherein, the carrier in the catalyst accounts for not less than 99 wt% of the total weight of the catalyst; preferably 99.6 wt%.
Wherein the metal in the catalyst comprises no more than 1 wt% of the total weight of the catalyst; preferably, it is 0.4 wt%.
The invention also provides a mononuclear-stannoxy-enriched tetrahedral silicon stannum molecular sieve supported metal catalyst.
Wherein the catalyst comprises a support and a metal.
The carrier is a silicon-tin molecular sieve rich in mononuclear tin-oxygen tetrahedron, and is selected from one or more of Sn-BEA, Sn-MFI, Sn-MOR, Sn-MWW and the like; preferably Sn-BEA.
The carrier accounts for not less than 99 wt% of the total weight of the catalyst; preferably 99.6 wt%.
The metal is selected from one or two of Pt, Pd, Rh and the like; preferably, it is Pt.
The metal comprises no more than 1 wt% of the total weight of the catalyst; preferably, it is 0.4 wt%.
The catalyst prepared by the invention has a complete Sn-BEA pore structure, the metal particles are in a nanometer shape, have ultra-small sizes (0.1-0.7nm), and are well encapsulated in the pores of the carrier silicon tin molecular sieve (as shown in figure 3A).
According to the invention, the noble metal nanoparticles are anchored by the highly dispersed four-coordinate Sn sites in the molecular sieve framework, the formed ultra-small noble metal-Sn clusters or crystal grains are stably confined in the molecular sieve pore channels, and the activity and the stability of the catalyst are greatly improved under the acidic synergistic effect of the ultra-small noble metal-Sn clusters or crystal grains and the remaining framework four-coordinate tin.
The invention also provides application of the mononuclear stannic oxide-rich tetrahedral silicon tin molecular sieve supported metal catalyst in direct dehydrogenation of low-carbon alkane.
Wherein the lower alkane comprises an alkane of 2 to 4 carbon atoms; preferably, it is propane.
Wherein the reaction temperature is 350-600 ℃; preferably, it is 500 ℃.
Wherein the reaction time is 1-500 h; preferably 200 h.
Wherein the mass space velocity in the reaction process is 0.5-120h-1(ii) a Preferably, it is 8h-1。
Wherein the pressure of the reaction is 1-10 atmospheres; preferably 1 atmosphere.
The catalyst of the invention is preferably used for the direct dehydrogenation of low-carbon alkane in a fixed bed.
The invention has the beneficial effects that: the mononuclear stannic oxide-rich tetrahedral silicon stannum molecular sieve supported metal catalyst prepared by the invention has ultrahigh catalytic activity and stability, and the selectivity of target olefin is up to more than 99%. The method has the advantages of less metal consumption, simple synthesis process, convenient operation, easy realization of industrial production and application, excellent catalytic performance, great saving of precious metal use cost and reduction of difficulty in subsequent product separation.
Drawings
FIG. 1 is XRD patterns of metal catalysts prepared in example 1 of the present invention and comparative example 1, wherein FIG. 1A is a wide-angle XRD full spectrum; FIG. 1B is a close-up view of a wide-angle XRD.
FIG. 2 is a CO-IR spectrum of the metal catalyst prepared in example 1 of the present invention and comparative example 1, wherein FIG. 2A is a total CO-IR spectrum; FIG. 2B is a partial enlarged view of CO-IR.
FIG. 3 is a STEM of a metal catalyst obtained in example 1 of the present invention, wherein FIG. 3A is a STEM of a metal catalyst obtained in example 1; FIG. 3B is a STEM chart of the metal catalyst prepared in comparative example 1.
FIG. 4 is a graph showing a stability test of catalysts of example 1 of the present invention and comparative example 1, wherein FIG. 4A is a graph showing a stability test of conversion of a substrate alkane; FIG. 4B is a graph of a product olefin selectivity stability test.
FIG. 5 is a nitrogen adsorption and desorption curve of the metal catalyst and the silicon-tin molecular sieve carrier prepared in example 1 of the present invention.
Detailed Description
The present invention will be described in further detail with reference to the following specific examples and the accompanying drawings. The procedures, conditions, experimental methods and the like for carrying out the present invention are general knowledge and common general knowledge in the art except for the contents specifically mentioned below, and the present invention is not particularly limited.
All the embodiments are operated according to the operation steps of the technical scheme.
In the following examples and comparative examples, carrier molecular sieves of different pore types were prepared by templating according to literature methods (Chinese journal of Catalysis,2015,36, 820; Materials Chemistry and Physics,2009,114,344, Catalysis Science & Technology,2017,7, 3151).
Example 1
(1) Roasting the Sn-BEA molecular sieve to obtain a dehydrated Si-Sn molecular sieve Sn-BEA without a template agent, wherein the molar ratio of Si to Sn in the carrier molecular sieve is 60, the roasting condition is that the roasting is carried out for 6 hours at 550 ℃ in an air atmosphere rich in water vapor, and the heating rate is 1.5 ℃/min;
(2) and (2) impregnating the material obtained in the step (1) with loaded metal Pt (the mass ratio of the metal Pt to the carrier is 0.005:1) by adopting a chloroplatinic acid wet method to prepare the metal catalyst precursor. Before the catalyst is used for alkane dehydrogenation reaction, reduction reaction is carried out in a hydrogen atmosphere containing 5% of propane at 500 ℃ to form the nano metal catalyst with molecular sieve pore channel restricted area. Then, propane is selected as a reactant, the metal catalyst prepared in the embodiment of the invention is used as a catalyst to carry out reduction reaction, the reaction temperature is 500 ℃, the reaction pressure is normal pressure, and the mass space velocity of the propane is 8h-1. The stable conversion rate of propane is 45%, the selectivity of propylene is 99%, and the catalytic stabilization period is as high as more than 200 hours.
The XRD characterization result (as shown in FIG. 1) shows that the metal catalyst does not have characteristic peaks of metal Pt and Pt-Sn, and shows that the obtained Pt particles or Pt-Sn particles are extremely small and highly dispersed (the dispersity is 78%).
The CO-IR characterization results (as shown in fig. 2) show that the metal catalyst has small particles of Pt and Pt-Sn species and no large metal particles.
STEM characterization results (as shown in fig. 3) show that the particles of the metal catalyst are nano-sized, have extremely small size (0.1-0.7nm), and are well encapsulated in the molecular sieve pores.
The catalyst stability test results (shown in figure 4) show that the metal catalyst has high activity at low temperature (the activity reaches 47 percent at 500 ℃), high olefin selectivity (99 percent) and high stability (more than 200 h).
Example 2
(1) Roasting the Sn-BEA molecular sieve to obtain a dehydrated Si-Sn molecular sieve Sn-BEA without a template agent, wherein the molar ratio of Si to Sn in the carrier molecular sieve is 60, the roasting condition is that the roasting is carried out for 6 hours at 550 ℃ in an air atmosphere rich in water vapor, and the heating rate is 1 ℃/min;
(2) and (2) carrying out ion exchange on the material obtained in the step (1) by adopting platinum nitrate to load metal Pt (the mass ratio of the metal Pt to the carrier is 0.01:1), and preparing the metal catalyst precursor. Before the catalyst is used for alkane dehydrogenation reaction, the catalyst is reduced under hydrogen atmosphere containing 5% propane at 500 ℃ to form the nano metal catalyst with molecular sieve pore-limited domain. Then, propane is selected as a reactant, the metal catalyst prepared in the embodiment of the invention is used as a catalyst to carry out reduction reaction, the reaction temperature is 500 ℃, the reaction pressure is normal pressure, and the mass space velocity of the propane is 8h-1. The stable conversion rate of propane is 47%, the selectivity of propylene is 99%, and the catalytic stabilization period is as high as more than 210 hours.
XRD characterization results show that the metal catalyst has characteristic peaks of metal Pt and Pt-Sn, and the obtained Pt and Pt-Sn have small particles and good dispersity.
Example 3
(1) Roasting the Sn-BEA molecular sieve to obtain a dehydrated Si-Sn molecular sieve Sn-BEA without a template agent, wherein the molar ratio of Si to Sn in the carrier molecular sieve is 60, the roasting condition is that the roasting is carried out for 6 hours at 550 ℃ in an air atmosphere rich in water vapor, and the heating rate is 1.5 ℃/min;
(2) and (2) impregnating the material obtained in the step (1) with loaded metal Pt (the mass ratio of the metal Pt to the carrier is 0.01:1) by adopting a chloroplatinic acid wet method to prepare the metal catalyst precursor. Before the catalyst is used for alkane dehydrogenation reaction, the catalyst is reduced under hydrogen atmosphere containing 5% propane at 500 ℃ to form the nano metal catalyst with molecular sieve pore-limited domain. Then, propane is selected as a reactant, the metal catalyst prepared in the embodiment of the invention is used as a catalyst to carry out reduction reaction, the reaction temperature is 500 ℃, the reaction pressure is normal pressure, and the mass space velocity of the propane is 8h-1. The stable conversion rate of propane is 53%, the selectivity of propylene is 99%, and the catalytic stabilization period is as high as more than 180 hours.
The XRD characterization result shows that the metal catalyst does not have characteristic peaks of metal Pt and Pt-Sn, and the obtained Pt particles or Pt-Sn particles are extremely small and highly dispersed.
Example 4
(1) Roasting the Sn-BEA molecular sieve to obtain a dehydrated Si-Sn molecular sieve Sn-BEA without a template agent, wherein the molar ratio of Si to Sn in the carrier molecular sieve is 150, the roasting condition is that the roasting is carried out for 6 hours at 550 ℃ in an air atmosphere rich in water vapor, and the heating rate is 1 ℃/min;
(2) and (2) adopting chloroplatinic acid loaded metal Pt (the mass ratio of the metal Pt to the carrier is 0.005:1) to prepare the metal catalyst precursor. Before the catalyst is used for alkane dehydrogenation reaction, the catalyst is reduced under hydrogen atmosphere containing 5% propane at 500 ℃ to form the nano metal catalyst with molecular sieve pore-limited domain. Then, propane is selected as a reactant, the metal catalyst prepared in the embodiment of the invention is used as a catalyst to carry out reduction reaction, the reaction temperature is 500 ℃, the reaction pressure is normal pressure, and the mass space velocity of the propane is 8h-1. The stable conversion rate of propane is 46%, the selectivity of propylene is 99%, and the catalytic stabilization period is as high as more than 180 hours.
XRD characterization results show that the metal catalyst has characteristic peaks of metal Pt and Pt-Sn, and the obtained Pt and Pt-Sn have small particles and good dispersity.
Example 5
(1) Roasting the Sn-BEA molecular sieve to obtain a dehydrated Si-Sn molecular sieve Sn-BEA without a template agent, wherein the molar ratio of Si to Sn in the carrier molecular sieve is 60, the roasting condition is that the roasting is carried out for 6 hours at 550 ℃ in an air atmosphere rich in water vapor, and the heating rate is 1 ℃/min;
(2) and (2) adopting palladium chloride acid to load metal Pd (the mass ratio of the metal Pd to the carrier is 0.005:1) to prepare the metal catalyst precursor. Before the catalyst is used for alkane dehydrogenation reaction, the catalyst is reduced under hydrogen atmosphere containing 5% propane at 500 ℃ to form the nano metal catalyst with molecular sieve pore-limited domain. Then, propane is selected as a reactant, the metal catalyst prepared in the embodiment of the invention is used as a catalyst to carry out reduction reaction, the reaction temperature is 500 ℃, the reaction pressure is normal pressure, and the mass space velocity of the propane is 8h-1. The stable conversion rate of propane is 40%, the selectivity of propylene is 99%, and the catalytic stabilization period is as high as more than 200 hours.
XRD characterization results show that the metal catalyst has characteristic peaks of metal Pd and Pd-Sn, and the obtained Pd and Pd-Sn have small particles and good dispersity.
Example 6
(1) Roasting the Sn-BEA molecular sieve to obtain a dehydrated Si-Sn molecular sieve Sn-BEA without a template agent, wherein the molar ratio of Si to Sn in the carrier molecular sieve is 60, the roasting condition is that the roasting is carried out for 6 hours at 550 ℃ in an air atmosphere rich in water vapor, and the heating rate is 1 ℃/min;
(2) and (2) loading metal Rh (the mass ratio of the metal Rh to the carrier is 0.005:1) on the material obtained in the step (1) by adopting ammonium chlororhodate to prepare a metal catalyst precursor. Before the catalyst is used for alkane dehydrogenation reaction, the catalyst is reduced under hydrogen atmosphere containing 5% propane at 500 ℃ to form the nano metal catalyst with molecular sieve pore-limited domain. Then, propane is selected as a reactant, the metal catalyst prepared in the embodiment of the invention is used as a catalyst to carry out reduction reaction, the reaction temperature is 500 ℃, the reaction pressure is normal pressure, and the mass space velocity of the propane is 8h-1. The stable conversion rate of propane is 45%, the selectivity of propylene is 99%, and the catalytic stabilization period is as high as more than 190 hours.
XRD characterization results show that the metal catalyst has characteristic peaks of metal Rh and Rh-Sn, and the obtained Rh and Rh-Sn have small particles and good dispersity.
Example 7
(1) Roasting the Sn-MFI molecular sieve to obtain a dehydrated Si-Sn molecular sieve Sn-MFI without a template agent, wherein the molar ratio of Si to Sn in the carrier molecular sieve is 100, the roasting condition is that the carrier molecular sieve is roasted for 6 hours at 550 ℃ in an air atmosphere rich in water vapor, and the heating rate is 1 ℃/min;
(2) and (2) impregnating the material obtained in the step (1) with loaded metal Pt (the mass ratio of the metal Pt to the carrier is 0.005:1) by adopting a chloroplatinic acid wet method to prepare the metal catalyst precursor. Before the catalyst is used for alkane dehydrogenation reaction, the catalyst is reduced under hydrogen atmosphere containing 5% propane at 500 ℃ to form the nano metal catalyst with molecular sieve pore-limited domain. Then, propane is selected as a reactant, the metal catalyst prepared in the embodiment of the invention is used as a catalyst to carry out reduction reaction, the reaction temperature is 500 ℃, the reaction pressure is normal pressure, and the mass space velocity of the propane is 8h-1. Stable conversion of propane is 40%, propylene selectivity99 percent and the catalytic stabilization period is as high as more than 200 hours.
The XRD characterization result shows that the metal catalyst does not have characteristic peaks of metal Pt and Pt-Sn, and the obtained Pt particles or Pt-Sn particles are extremely small and highly dispersed.
Example 8
(1) Roasting the Sn-MWW molecular sieve to obtain a dehydrated Si-Sn molecular sieve Sn-MWW without a template agent, wherein the molar ratio of Si to Sn in the carrier molecular sieve is 100, the roasting condition is that the carrier molecular sieve is roasted for 6 hours at 550 ℃ in an air atmosphere rich in water vapor, and the heating rate is 1 ℃/min;
(2) and (2) impregnating the material obtained in the step (1) with loaded metal Pt (the mass ratio of the metal Pt to the carrier is 0.005:1) by adopting a chloroplatinic acid wet method to prepare the metal catalyst precursor. Before the catalyst is used for alkane dehydrogenation reaction, the catalyst is reduced under hydrogen atmosphere containing 5% propane at 500 ℃ to form the nano metal catalyst with molecular sieve pore-limited domain. Then, propane is selected as a reactant, the metal catalyst prepared in the embodiment of the invention is used as a catalyst to carry out reduction reaction, the reaction temperature is 500 ℃, the reaction pressure is normal pressure, and the mass space velocity of the propane is 8h-1. The stable conversion rate of propane is 39%, the selectivity of propylene is 99%, and the catalytic stabilization period is as high as more than 180 hours.
The XRD characterization result shows that the metal catalyst does not have characteristic peaks of metal Pt and Pt-Sn, and the obtained Pt particles or Pt-Sn particles are extremely small and highly dispersed.
Example 9
(1) Roasting the Sn-BEA molecular sieve to obtain a dehydrated Si-Sn molecular sieve Sn-BEA without a template agent, wherein the molar ratio of Si to Sn in the carrier molecular sieve is 60, the roasting condition is that the roasting is carried out for 6 hours at 550 ℃ in an air atmosphere rich in water vapor, and the heating rate is 1 ℃/min;
(2) and (2) impregnating the material obtained in the step (1) with loaded metal Pt (the mass ratio of the metal Pt to the carrier is 0.005:1) by adopting a chloroplatinic acid wet method to prepare the metal catalyst precursor. Before the catalyst is used for alkane dehydrogenation reaction, the catalyst is reduced in hydrogen atmosphere containing 10% propane at 500 ℃ to form the nano metal catalyst with molecular sieve pore-limited domain. Propane was then selected as the reactant, in accordance with the examples of the present inventionThe prepared metal catalyst is used as a catalyst for reduction reaction, the reaction temperature is 570 ℃, the reaction pressure is normal pressure, and the mass space velocity of propane is 8h-1. The stable conversion rate of propane is 46%, the selectivity of propylene is 99%, and the catalytic stabilization period is as high as 230 hours or more.
Example 10
(1) Roasting the Sn-BEA molecular sieve to obtain a dehydrated Si-Sn molecular sieve Sn-BEA without a template agent, wherein the molar ratio of Si to Sn in the carrier molecular sieve is 60, the roasting condition is that the roasting is carried out for 6 hours at 550 ℃ in an air atmosphere rich in water vapor, and the heating rate is 1 ℃/min;
(2) and (2) impregnating the material obtained in the step (1) with loaded metal Pt (the mass ratio of the metal Pt to the carrier is 0.005:1) by adopting a chloroplatinic acid wet method to prepare the metal catalyst precursor. Before the catalyst is used for alkane dehydrogenation reaction, the catalyst is reduced under hydrogen atmosphere containing 5% of propane at 570 ℃ to form the nano metal catalyst with molecular sieve pore-limited domain. Then, propane is selected as a reactant, the metal catalyst prepared in the embodiment of the invention is used as a catalyst to carry out reduction reaction, the reaction temperature is 570 ℃, the reaction pressure is normal pressure, and the mass space velocity of the propane is 20h-1. The stable conversion rate of propane is 60%, the selectivity of propylene is 99%, and the catalytic stabilization period is as high as more than 150 hours.
Example 11
(1) Roasting the Sn-BEA molecular sieve to obtain a dehydrated Si-Sn molecular sieve Sn-BEA without a template agent, wherein the molar ratio of Si to Sn in the carrier molecular sieve is 60, the roasting condition is that the roasting is carried out for 6 hours at 550 ℃ in an air atmosphere rich in water vapor, and the heating rate is 1 ℃/min;
(2) and (2) impregnating the material obtained in the step (1) with loaded metal Pt (the mass ratio of the metal Pt to the carrier is 0.005:1) by adopting a chloroplatinic acid wet method to prepare the metal catalyst precursor. Before the catalyst is used for alkane dehydrogenation reaction, the catalyst is reduced in a hydrogen atmosphere at 530 ℃ to form the nano metal catalyst with molecular sieve pore-limited domains. Then isobutane is selected as a reactant, the metal catalyst prepared in the embodiment of the invention is used as a catalyst to perform reduction reaction, the reaction temperature is 530 ℃, the reaction pressure is normal pressure, and the mass space velocity of isobutane is 8h-1. The stable conversion rate of isobutane was 58%The selectivity of the butene is more than 95 percent, and the catalytic stabilization period is as high as more than 200 hours.
Example 12
(1) Roasting the Sn-BEA molecular sieve to obtain a dehydrated Si-Sn molecular sieve Sn-BEA without a template agent, wherein the molar ratio of Si to Sn in the carrier molecular sieve is 60, the roasting condition is that the roasting is carried out for 6 hours at 550 ℃ in an air atmosphere rich in water vapor, and the heating rate is 1.5 ℃/min;
(2) and (2) impregnating the material obtained in the step (1) with loaded metal Pt (the mass ratio of the metal Pt to the carrier is 0.005:1) by adopting a chloroplatinic acid wet method to prepare the metal catalyst precursor. Before the catalyst is used for alkane dehydrogenation reaction, reduction reaction is carried out in a hydrogen atmosphere containing 5% of propane at 500 ℃ to form the nano metal catalyst with molecular sieve pore channel restricted area. Then, propane is selected as a reactant, the metal catalyst prepared in the embodiment of the invention is used as a catalyst to carry out reduction reaction, the reaction temperature is 500 ℃, the reaction pressure is 2 atm, and the mass space velocity of the propane is 8h-1. The stable conversion rate of propane is 55%, the selectivity of propylene is 97%, and the catalytic stabilization period is as high as more than 200 hours.
Comparative example 1
(1) And (2) roasting the pure silicon molecular sieve to obtain a dehydrated molecular sieve Si-BEA without a template agent, wherein the roasting condition is that the molecular sieve Si-BEA is roasted for 6 hours at 550 ℃ in an air atmosphere rich in water vapor, and the heating rate is 1 ℃/min.
(3) And (2) impregnating the material obtained in the step (1) with loaded metal Pt (the mass ratio of the metal Pt to the carrier is 0.005:1) by adopting a wet method to prepare the metal catalyst precursor. Before the dehydrogenation reaction of alkane, the metal catalyst is reduced in hydrogen atmosphere containing 5% propane at 500 ℃ to obtain the metal catalyst. Then selecting propane as a reactant, and carrying out reduction reaction by using the metal catalyst prepared in the comparative example as a catalyst, wherein the reaction temperature is 500 ℃, the reaction pressure is normal pressure, and the mass space velocity of the propane is 8h-1. The initial conversion of propane was 47% and the propylene selectivity was 60%, with rapid catalyst deactivation.
The XRD characterization result (figure 1) shows that the metal catalyst has a characteristic peak of metal Pt, which indicates that the obtained Pt particles are large and have poor dispersity.
The CO-IR characterization results (fig. 2) show the presence of large Pt particles for this metal catalyst.
STEM characterization results (fig. 3) show that the particle size of the metal catalyst is very large and is almost outside the molecular sieve channels.
The catalyst stability test results (fig. 4) show that the metal catalyst has low activity, low olefin selectivity and low stability.
Comparative example 2
(1) And (2) roasting the pure silicon molecular sieve to obtain a dehydrated molecular sieve Si-BEA without a template agent, wherein the roasting condition is that the molecular sieve Si-BEA is roasted for 6 hours at 550 ℃ in an air atmosphere rich in water vapor, and the heating rate is 1 ℃/min.
(3) And (2) impregnating the material obtained in the step (1) with loaded metal Pt (the mass ratio of the metal Pt to the carrier is 0.005:1) by adopting a wet method to prepare the metal catalyst precursor. Before the catalyst is used for alkane dehydrogenation reaction, the catalyst is reduced at 500 ℃ in a hydrogen atmosphere containing 5% of isobutane to obtain the metal catalyst. Then selecting isobutane as a reactant, and carrying out reduction reaction by using the metal catalyst prepared in the comparative example as a catalyst, wherein the reaction temperature is 500 ℃, the reaction pressure is normal pressure, and the mass airspeed of the isobutane is 8h-1. The initial conversion rate of isobutane was 39%, the initial selectivity of isobutene was 55%, and the catalyst was rapidly deactivated.
The XRD characterization result shows that the metal catalyst has a characteristic peak of metal Pt, which indicates that the obtained Pt particles are large and have poor dispersion degree.
The above description is only for the preferred embodiment of the present invention, and the protection content of the present invention is not limited to the above embodiment. Variations and advantages that may occur to those skilled in the art may be incorporated into the invention without departing from the spirit and scope of the inventive concept, which is set forth in the following claims.

Claims (13)

1. A method for preparing a mononuclear tin-oxygen-enriched tetrahedral silicon tin molecular sieve supported metal catalyst is characterized by comprising the following steps:
(1) guiding the template agent to the prepared silicon-tin molecular sieve for roasting to obtain a silicon-tin molecular sieve carrier which does not contain the template agent and is rich in mononuclear tin-oxygen tetrahedrons;
(2) loading a metal precursor on the silicon-tin molecular sieve carrier prepared in the step (1) to obtain a metal catalyst precursor; and then carrying out controlled reduction reaction on the metal catalyst precursor to obtain the mononuclear tin-oxygen-enriched tetrahedral silicon tin molecular sieve supported metal catalyst.
2. The method according to claim 1, characterized in that it comprises in particular the steps of:
(1) guiding the template agent to the prepared silicon-tin molecular sieve, and roasting at high temperature in air atmosphere to remove the template agent and water to obtain a silicon-tin molecular sieve carrier which does not contain the template agent and is rich in mononuclear tin-oxygen tetrahedrons;
(2) loading a metal precursor on the silicon-tin molecular sieve carrier prepared in the step (1) to obtain a loaded metal catalyst precursor; and then performing controlled reduction reaction on the metal catalyst precursor in a hydrogen atmosphere containing low-carbon alkane to obtain the mononuclear tin-oxygen-enriched tetrahedral silicon tin molecular sieve supported metal catalyst.
3. The process of claim 1 or 2, wherein in step (1), the silicon-tin molecular sieve is selected from one or more of Sn-BEA, Sn-MFI, Sn-MOR, Sn-MWW; and/or the mole ratio of silicon to tin in the silicon-tin molecular sieve is (30-200): 1.
4. the method according to claim 1 or 2, wherein in the step (1), the roasting condition is that the roasting is carried out for 2-12 hours at 400-600 ℃ in an air atmosphere rich in water vapor, and the temperature rising rate is 1-2 ℃/min.
5. The method according to claim 1 or 2, wherein in the step (2), the metal precursor comprises one or two of chloroplatinic acid, ammonium chloropalladate, ammonium chlororhodate, platinum nitrate, palladium nitrate and rhodium sulfate; and/or the mass ratio of the metal precursor to the carrier is (99-99.95): (0.05-1).
6. The method of claim 1 or 2, wherein in the step (2), the volume ratio of the low-carbon alkane to the hydrogen is (0-10): (90-100); and/or the lower alkane is an alkane with 2-4 carbons.
7. The method as claimed in claim 1 or 2, wherein in step (2), the temperature of the reduction reaction is 150-600 ℃; and/or the time of the reduction reaction is 1-4 h.
8. The method according to claim 1 or 2, wherein in the step (2), the reduction reaction is finished and then the step of purging the metal catalyst with nitrogen is further included, and the purging time is 1-4 h.
9. A mononuclear tin oxide-rich tetrahedral silicon tin molecular sieve supported metal catalyst prepared according to the method of any one of claims 1 to 8.
10. A mononuclear tin oxygen-enriched tetrahedral silicon tin molecular sieve supported metal catalyst, which is characterized by comprising a carrier and a metal; the carrier is a silicon-tin molecular sieve rich in mononuclear tin-oxygen tetrahedron, and is selected from one or more of Sn-BEA, Sn-MFI, Sn-MOR and Sn-MWW; and/or the metal is selected from one or two of Pt, Pd and Rh.
11. The catalyst of claim 10 wherein the support comprises not less than 99 wt% of the total weight of the catalyst; the metal comprises no more than 1 wt% of the total weight of the catalyst.
12. The use of the mononuclear tin oxide-rich tetrahedral silicon tin molecular sieve supported metal catalyst according to claim 9 or 10 in the direct dehydrogenation reaction of lower alkanes.
13. The use of claim 12, wherein the lower alkane is an alkane having 2 to 4 carbon atoms(ii) a And/or the temperature of the reaction is 350-600 ℃; and/or the mass space velocity in the reaction process is 0.5-120h-1(ii) a And/or the pressure of the reaction is 1 to 10 atmospheres.
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