CN117181281A

CN117181281A - Encapsulated metal zeolite catalyst and its preparation method and application

Info

Publication number: CN117181281A
Application number: CN202311166034.3A
Authority: CN
Inventors: 王石维; 张飞; 石丙千
Original assignee: Ningbo Concong Technology Service Co ltd; Zhejiang Research Institute Of Tianjin University
Current assignee: Ningbo Concong Technology Service Co ltd; Zhejiang Research Institute Of Tianjin University
Priority date: 2023-09-11
Filing date: 2023-09-11
Publication date: 2023-12-08

Abstract

The application discloses a packaged metal zeolite catalyst, a preparation method and application thereof, wherein the catalyst comprises zeolite; doping metal, doping and dispersing in the framework of the zeolite; active metal distributed in the pore canal and cage structure of the zeolite; wherein the active metal comprises one or a combination of two of active metal clusters and active metal nanoparticles. The encapsulated metal zeolite catalyst of the application improves the conversion rate of glycerin and the selectivity of DHA as a product based on the synergistic effect of active metal and zeolite, the improving effect of doped metal on the synergistic effect and the improving effect of doped metal on DHA yield, and can realize the preparation of DHA by selective catalytic glycerin oxidation, wherein the DHA content in the glycerin oxidation product is up to 72.2%.

Description

Encapsulated metal zeolite catalyst and its preparation method and application

Technical Field

The application belongs to the technical field of oxidation catalysis, and particularly relates to a packaged metal zeolite catalyst, and a preparation method and application thereof.

Background

Glycerol is a major byproduct of biodiesel production, producing 1 pound of crude glycerol per 10 pounds of biodiesel, and the economic value of crude glycerol as a biodiesel byproduct is also low. For this reason, various catalytic technologies including oxidation, hydrogenolysis, reforming, dehydration, etc. have been developed for producing value-added compounds from crude glycerin as a raw material. The selective catalytic oxidation of glycerol to generate 1, 3-Dihydroxyacetone (DHA) has important significance, and the DHA has wide application range and wide market application prospect, is an important chemical raw material, and can be used as a platform molecule for producing cosmetics, fine chemicals and the like.

The encapsulated zeolite catalyst has the advantages of simple preparation process, low cost, excellent recycling performance and better industrial prospect, so the encapsulated zeolite catalyst becomes a research hot spot for catalyzing the selective oxidation of glycerol. However, since the three hydroxyl groups in the glycerol molecule are basically similar in nature, the activation of the primary and secondary hydroxyl groups is difficult to control in glycerol conversion, especially in selective oxidation reaction, and the selective catalysis of glycerol to form DHA is difficult. Thus, preparing a highly active, highly selective zeolite catalyst for the selective catalytic oxidation of glycerol to DHA remains a challenge.

Disclosure of Invention

The application aims to provide an encapsulated metal zeolite catalyst and a preparation method and application thereof, and aims to solve the technical problems that in the prior art, as three hydroxyl groups in glycerol molecules are basically similar in nature, in glycerol conversion, especially in selective oxidation reaction, activation of primary and secondary hydroxyl groups is difficult to control, and DHA is difficult to selectively catalyze glycerol.

In order to achieve the above purpose, the application adopts a technical scheme that:

provided is a packaged metal zeolite catalyst comprising:

a zeolite;

doping metal, doping and dispersing in the framework of the zeolite;

active metal distributed in the pore canal and cage structure of the zeolite;

wherein the active metal comprises one or a combination of two of active metal clusters and active metal nanoparticles.

In one or more embodiments, the doping metal includes one or more combinations of Sn, al, mn, sb, and the content of the doping metal in the encapsulated metal zeolite catalyst is 0.01 to 4.0wt%.

Preferably, the doping metal is Sn.

In one or more embodiments, the active metal comprises one or more combinations of Ru, pd, au, pt, and the active metal component is present in the encapsulated metal zeolite catalyst in an amount of 0.01 to 5.0wt%.

Preferably, the active metal includes one of Pt, au, pd.

In one or more embodiments, the active metal nanoparticles have a particle size of 3.0 to 5.5nm.

In one or more embodiments, the zeolite is in the form of ZSM-5, beta, FAU, SSZ-13, MOR or MWW and has a specific surface area of from 150 to 300m ² Per gram, the pore volume of the pore canal of the zeolite is 0.07-0.15 cm ³ /g。

the preparation method of the encapsulated metal zeolite catalyst according to any one of the above embodiments comprises the following steps:

uniformly mixing an active metal salt precursor and a doped metal salt precursor with an aqueous solution containing organic amine respectively to obtain a complex active metal salt solution and a complex doped metal salt solution, wherein the active metal salt precursor is soluble salt of the active metal, and the doped metal salt precursor is soluble salt of the doped metal;

mixing the complexing active metal salt solution, the complexing doped metal salt solution and zeolite synthesis mother liquor, evaporating to obtain reaction gel, and performing hydrothermal reaction on the reaction gel to obtain a catalyst precursor;

and (3) sequentially centrifugally washing, drying and roasting the catalyst precursor at high temperature to obtain the encapsulated metal zeolite catalyst.

In one or more embodiments, the organic amine comprises one or more combinations of ammonia, ethylenediamine, n-propylamine, t-butylamine, and trimethylamine, the molar ratio of the organic amine to the active metal salt precursor is (1-600): 1, and the molar ratio of the doped metal salt precursor to the active metal salt precursor is (0.1-5): 1.

preferably, the molar ratio of the organic amine to the active metal salt precursor is (20-200) to 1.

Preferably, the molar ratio of the doped metal salt precursor to the active metal salt precursor is (1-3): 1.

in one or more embodiments, the zeolite synthesis mother liquor comprises a templating agent comprising one or more combinations of tetrapropylammonium hydroxide, isopropylamine, di-N-propylamine, N-trimethylsteel alkyl ammonium hydroxide, triethylamine, morpholine and a silicon source comprising one or more combinations of tetraethyl orthosilicate, sodium silicate, water glass, silica gel; the molar ratio of the active metal salt precursor to the silicon source is (0.0005-0.2) to 1.

Preferably, the molar ratio of the active metal salt precursor to the silicon source is (0.001-0.05) to 1.

Preferably, the molar ratio of the active metal salt precursor to the silicon source is (0.001-0.01) to 1.

In one or more embodiments, the step of mixing the complex active metal salt solution, the complex doped metal salt solution and the zeolite synthesis mother solution, evaporating to obtain reaction gel, and performing a hydrothermal reaction on the reaction gel to obtain a catalyst precursor, wherein the temperature of the hydrothermal reaction is 120-300 ℃ and the reaction time is 1-20 h.

Preferably, the temperature of the hydrothermal reaction is 200-270 ℃ and the reaction time is 1-5 h.

In one or more embodiments, in the steps of sequentially centrifugally washing, drying and high-temperature roasting the catalyst precursor, the centrifugally washed detergent comprises one or more of water, acetone and ethanol, and the high-temperature roasting is specifically carried out in an air atmosphere at a heating rate of 1-5 ℃/min to 400-700 ℃ for 1-12 h.

Preferably, the high-temperature roasting is specifically carried out by heating to 500-700 ℃ at a heating rate of 3-5 ℃/min in an air atmosphere and roasting for 3-5 h.

the application of the encapsulated metal zeolite catalyst according to any one of the embodiments or the encapsulated metal zeolite catalyst prepared by the preparation method according to any one of the embodiments in the preparation of dihydroxyacetone by catalytic selective oxidation of glycerol is provided.

Compared with the prior art, the application has the beneficial effects that:

the encapsulated metal zeolite catalyst of the application is based on the synergistic effect of active metal and zeolite, the synergistic effect improving effect of doped metal and the DHA yield improving effect of doped metal, improves the conversion rate of glycerin and the selectivity of DHA as a product, and can realize the preparation of DHA by selective catalytic glycerin oxidation, wherein the DHA content in the glycerin oxidation product is up to 72.2%;

the encapsulated metal zeolite catalyst has the advantages of green and nontoxic property, low cost, high yield of target products, good catalytic stability and the like, can be popularized to a plurality of other catalytic reaction systems, and has wide application prospect;

according to the preparation method, the active metal salt precursor and the organic amine aqueous solution are mixed, so that the active metal precursor can be kept in a stable ionic state under the action of the ligand in an alkaline environment, and stable packaging and size control of the active metal are realized in the subsequent hydrothermal reaction; by mixing the doped metal salt precursor with an aqueous organic amine solution, the doped metal can be formed into a complex with the ligand, which complex can be converted to a hydroxide in a hydrothermal reaction, thereby achieving the dispersion of the doped metal in the zeolite framework.

Drawings

FIG. 1 is a schematic flow chart of one embodiment of a process for preparing an encapsulated zeolite catalyst of the present application;

FIG. 2 is a representation of the catalyst prepared in example 1, where a is a TEM image of the catalyst prepared in example 1, b is an enlarged image of a, and c is an analysis image of the particle size distribution of the metal nanoparticles of the catalyst prepared in example 1;

FIG. 3 is a representation of the catalyst prepared in example 2, wherein a1 is a TEM image of the catalyst prepared in example 2 and a2 is a graph of the particle size distribution analysis of the metal nanoparticles of the catalyst prepared in example 2;

FIG. 4 is a representation of the catalyst prepared in example 3, wherein b1 is a TEM image of the catalyst prepared in example 3 and b2 is a graph of the particle size distribution analysis of the metal nanoparticles of the catalyst prepared in example 3;

FIG. 5 is a representation of the catalyst prepared in comparative example 1, wherein c1 is a TEM image of the catalyst prepared in comparative example 1 and c2 is an analysis image of the metal nanoparticle particle size distribution of the catalyst prepared in comparative example 1;

FIG. 6 is a graph showing the characterization of the catalyst prepared in comparative example 2, wherein d1 is a TEM image of the catalyst prepared in comparative example 2, and d2 is a graph showing the analysis of the particle size distribution of the metal nanoparticles of the catalyst prepared in comparative example 2;

FIG. 7 is a TEM image of the catalyst prepared in comparative example 3;

FIG. 8 is a graph showing the mass fraction of the experimental reaction product of effect example 2 of the present application;

FIG. 9 is a graph showing the mass fraction of the experimental reaction product of effect example 3 of the present application;

FIG. 10 is a graph showing the mass fraction of the experimental reaction product of effect example 4 of the present application;

FIG. 11 is a graph showing the mass fraction of the experimental reaction product of effect example 5 of the present application.

Detailed Description

In the biodiesel production process, a large amount of glycerin byproducts exist, and crude glycerin as a byproduct has low economic value. In order to optimize the resource application and improve the economic value, various catalytic technologies including oxidation, hydrogenolysis, reforming, dehydration and the like have been developed for producing value-added compounds by using crude glycerol as a raw material. The selective catalytic oxidation of glycerol as a raw material to generate 1, 3-Dihydroxyacetone (DHA) has important significance, and the DHA has wide application range and wide market application prospect, is an important chemical raw material, and can be used as a platform molecule for producing cosmetics, fine chemicals and the like.

The encapsulated zeolite catalyst has the advantages of simple catalyst preparation process, low cost, excellent catalyst recycling performance and better industrial prospect, so the encapsulated zeolite catalyst becomes a research hot spot for catalyzing the selective oxidation of glycerin. However, since the three hydroxyl groups in the glycerol molecule are substantially similar in nature, the activation of the primary hydroxyl groups is difficult to control in glycerol conversion, especially in selective oxidation. Thus, preparing a highly active, highly selective zeolite catalyst for the selective catalytic oxidation of glycerol to DHA remains a challenge.

In order to solve the problems, the applicant develops a novel encapsulated zeolite catalyst which can be applied to the preparation of DHA by the selective oxidation of catalytic glycerin, and has the advantages of low specific cost, high yield of target products and high catalytic stability, thereby effectively improving the economic value.

The encapsulated zeolite catalysts of the present application include zeolite, doped metal and active metal.

Wherein the doping metal is doped and dispersed in the framework of the zeolite; the active metal is dispersed in the pore canal and cage structure of the zeolite and can comprise one or two of active metal clusters and active metal nano particles.

The doped metal dispersed in the zeolite framework can improve the synergistic effect of the active metal and the zeolite, thereby improving the catalytic capability of the active metal on glycerol oxidation. Furthermore, due to the electronic interaction between the active metal and the doped metal, glyceraldehyde can be inhibited from being further oxidized into glyceric acid, and meanwhile, the selectivity of DHA can be improved by doping Lewis acid sites generated in the metal in zeolite, so that the yield of DHA is improved, and the purpose of preparing DHA by selectively catalyzing glycerol oxidation is realized.

In one embodiment, the doping metal may include Sn, al, mn, sb. More preferably, the doping metal may be Sn.

In one embodiment, in order to ensure the effect of improving the yield of DHA by the doping metal, the content of the doping metal in the encapsulated metal zeolite catalyst may be 0.01 to 4.0wt%.

In one embodiment, the active metal may comprise one or more combinations of Ru, pd, au, pt. More preferably, the active metal may include one of Pt, au, pd.

In one embodiment, the content of the active metal component in the encapsulated metal zeolite catalyst may be 0.01 to 5.0wt% in order to secure the oxidation catalytic performance of the active metal on glycerin.

In one embodiment, to ensure that the catalyst has sufficient catalytic sites, the zeolite may be in the form of ZSM-5, beta, FAU, SSZ-13, MOR or MWW and the specific surface area of the zeolite may be in the range of 150 to 300m ² The pore volume of the pore canal of the zeolite can be 0.07-0.15 cm ³ /g。

In one embodiment, in order to ensure the oxidation catalytic performance of the active metal on glycerin, the particle size of the active metal nanoparticles may be 3.0 to 5.5nm.

The encapsulated zeolite catalyst disclosed by the application has the advantages that the conversion rate of glycerin and the selectivity of DHA as a product are improved based on the synergistic effect of active metal and zeolite, the synergistic effect improving effect of doped metal and the DHA yield improving effect of doped metal, and DHA can be prepared by selectively catalyzing the oxidation of glycerin; has the advantages of green non-toxicity, low cost, high yield of target products, good catalytic stability and the like, can be popularized to a plurality of other catalytic reaction systems, and has wide application prospect.

The application also provides a preparation method of the encapsulated zeolite catalyst, referring to fig. 1, fig. 1 is a schematic flow chart of an embodiment of the preparation method of the encapsulated zeolite catalyst of the application.

The preparation method comprises the following steps:

and S100, uniformly mixing the active metal salt precursor and the doped metal salt precursor with an aqueous solution containing organic amine respectively to obtain a complex active metal salt solution and a complex doped metal salt solution.

Wherein the active metal salt precursor is a soluble salt of an active metal, and the doped metal salt precursor is a soluble salt of a doped metal.

In one embodiment, the soluble salt may be a chloride salt, and in other embodiments, the soluble salt may be a salt soluble in other aqueous solutions such as nitrate, and the effects of this embodiment can be achieved.

In one embodiment, the organic amine may include one or more combinations of aqueous ammonia, ethylenediamine, n-propylamine, t-butylamine, and trimethylamine, and the molar ratio of organic amine to active metal salt precursor may be (1-600): 1, the molar ratio of the doped metal salt precursor to the active metal salt precursor may be (0.1-5): 1.

preferably, the molar ratio of organic amine to active metal salt precursor may be (20-200): 1.

preferably, the molar ratio of the doped metal salt precursor to the active metal salt precursor may be (1-3): 1.

s200, mixing the complex active metal salt solution, the complex doped metal salt solution and the zeolite synthesis mother solution, evaporating to obtain reaction gel, and performing hydrothermal reaction on the reaction gel to obtain a catalyst precursor.

The zeolite synthesis mother liquor can comprise a template agent and a silicon source, wherein the template agent can comprise one or more of tetrapropylammonium hydroxide, isopropylamine, di-N-propylamine, N, N, N-trimethyl steel alkyl ammonium hydroxide, triethylamine and morpholine, and the silicon source can comprise one or more of tetraethoxysilane, sodium silicate, water glass and silica gel.

In one embodiment, the molar ratio of the active metal salt precursor to the silicon source may be (0.001 to 0.05) to 1 in order to ensure the catalytic oxidation performance of the catalyst.

More preferably, the molar ratio of the active metal salt precursor to the silicon source may be (0.001 to 0.01) to 1.

In one embodiment, the evaporation may be performed in a rotary evaporator, in order to remove most of the water and ethanol, and in other embodiments, other evaporation may be performed, so that the effect of this embodiment can be achieved.

In one embodiment, the hydrothermal reaction may be performed at a temperature of 120 to 300 ℃ for a reaction time of 1 to 20 hours.

More preferably, the temperature of the hydrothermal reaction may be 200 to 270 ℃ and the reaction time may be 1 to 5 hours.

It can be appreciated that by mixing the active metal salt precursor with the aqueous organic amine solution, the active metal precursor can be kept in a stable ionic state under the action of the ligand in an alkaline environment, so that stable packaging and size control of the active metal are realized in the subsequent hydrothermal reaction;

by mixing the doped metal salt precursor with an aqueous organic amine solution, the doped metal can be formed into a complex with the ligand, which complex can be converted to a hydroxide in a hydrothermal reaction, thereby achieving the dispersion of the doped metal in the zeolite framework.

S300, sequentially centrifugally washing, drying and roasting the catalyst precursor at high temperature to obtain the encapsulated metal zeolite catalyst.

In one embodiment, the above-described centrifugally washed detergent may be a detergent comprising one or more of water, acetone, ethanol. Preferably, the detergent may be water.

In one embodiment, the high temperature calcination may be specifically performed by heating to 400 to 700 ℃ at a heating rate of 1 to 5 ℃/min in an air atmosphere and calcining for 1 to 12 hours.

More preferably, the high-temperature roasting may be specifically carried out by raising the temperature to 500-700 ℃ at a heating rate of 3-5 ℃/min in an air atmosphere and roasting for 3-5 hours.

The following describes the advantageous effects of the technical scheme of the present application in further detail in conjunction with specific examples.

Example 1:

an encapsulated zeolite catalyst Pt@Sn-MFI-80 is prepared from the following raw materials in molar ratio: 1.0 tetraethoxysilane: 0.4 tetrapropylammonium hydroxide: 35.0 deionized water: 0.003 platinum chloride: 0.0057 stannic chloride: 0.0174 ethylenediamine.

The preparation method comprises the following steps:

mixing tetrapropylammonium hydroxide with water, continuously stirring, adding tetraethoxysilane, and completely hydrolyzing to obtain a solution A; fully mixing and stirring platinum chloride, ethylenediamine and water to obtain a solution B; fully mixing and stirring tin chloride, ethylenediamine and water to obtain a solution C;

dropping the solution B and the solution C into the solution A, uniformly stirring, putting into a rotary evaporator, evaporating at 70 ℃ for 1h, and removing most of water and ethanol to obtain reaction gel;

transferring the reaction gel into a hydrothermal reaction kettle, and crystallizing for 3 hours at 240 ℃; and (3) centrifugally washing the crystallized solid with water for three times, drying overnight at 105 ℃, and then heating the dried product to 550 ℃ at a heating rate of 5 ℃/min under an air atmosphere to bake for 4 hours to obtain the product Pt@Sn-MFI-80 zeolite catalyst.

Example 2:

the encapsulated zeolite catalyst Pt@Sn-MFI-100 was prepared in substantially the same manner as in example 1, except for the amounts of tin chloride and ethylenediamine used in the feedstock, specifically, in example 2, the following molar ratios of the feedstock were used: 1.0 tetraethoxysilane: 0.4 tetrapropylammonium hydroxide: 35.0 deionized water: 0.003 platinum chloride: 0.01 stannic chloride: 0.026 ethylenediamine.

Example 3:

the encapsulated zeolite catalyst Pt@Sn-MFI-175 was prepared in substantially the same manner as in example 1, except that the amounts of tin chloride and ethylenediamine used in the feed, specifically, in example 3, were prepared using the following molar ratios of feed: 1.0 tetraethoxysilane: 0.4 tetrapropylammonium hydroxide: 35.0 deionized water: 0.003 platinum chloride: 0.0125 stannic chloride: 0.031 ethylene diamine.

Comparative example 1:

the encapsulated zeolite catalyst Pt@S-1 is prepared from the following raw materials in molar ratio: 1.0 tetraethoxysilane: 0.4 tetrapropylammonium hydroxide: 35.0 deionized water: 0.003 platinum chloride: 0.006 ethylenediamine.

The preparation method comprises the following steps:

mixing tetrapropylammonium hydroxide with water, continuously stirring, adding tetraethoxysilane, and completely hydrolyzing to obtain a solution A; fully mixing and stirring platinum chloride, ethylenediamine and water to obtain a solution B;

dropping the solution B into the solution A, uniformly stirring, putting into a rotary evaporator, evaporating at 70 ℃ for 1h, and removing most of water and ethanol to obtain reaction gel;

transferring the reaction gel into a hydrothermal reaction kettle, and crystallizing for 3 hours at 240 ℃; and (3) centrifugally washing the crystallized solid with water for three times, drying overnight at 105 ℃, and then heating the dried product to 550 ℃ at a heating rate of 5 ℃/min under an air atmosphere to bake for 4 hours to obtain the product Pt@S-1 zeolite catalyst.

Comparative example 2:

Pt/SiO ₂ The supported catalyst is prepared by the following steps:

dissolving platinum chloride and a surfactant polyvinylpyrrolidone (PVP) in ethylene glycol, and stirring for 1h at 50 ℃ under a nitrogen atmosphere;

injecting sodium borohydride solution dispersed in ethanol into the solution, and reducing Pt species to obtain black solid products, namely Pt nano particles;

centrifuging and washing Pt nano particles with a small amount of glycol and acetone for three times, and dispersing the Pt nano particles in ethanol;

adding silicon dioxide into the ethanol solution, stirring for 5h under nitrogen atmosphere at 80 ℃, and then heating the obtained gray product to 500 ℃ at a heating rate of 5 ℃/min under air atmosphere to bake for 3h to obtain a product Pt/SiO with Pt load of 1.0wt% ₂ Supported catalysts.

Comparative example 3:

a catalyst Sn-MFI prepared from the following raw materials in molar ratio: 1.0 tetraethoxysilane: 0.4 tetrapropylammonium hydroxide: 35.0 deionized water: 0.0125 stannic chloride: 0.025 ethylenediamine.

The preparation method comprises the following steps:

mixing tetrapropylammonium hydroxide with water, continuously stirring, adding tetraethoxysilane, and completely hydrolyzing to obtain a solution A; fully mixing and stirring tin chloride, ethylenediamine and water to obtain a solution B;

transferring the reaction gel into a hydrothermal reaction kettle, and crystallizing for 3 hours at 240 ℃; and (3) centrifugally washing the solid obtained after crystallization with water for three times, drying overnight at 105 ℃, and then heating the dried product to 550 ℃ at a heating rate of 5 ℃/min under an air atmosphere to bake for 4 hours to obtain the product Sn-MFI catalyst.

Effect example 1:

characterization analysis was performed on the catalysts prepared in examples 1 to 3 and comparative examples 1 to 3, resulting in fig. 2 to 7.

Wherein, fig. 2 is a characterization diagram of the catalyst prepared in example 1, wherein a is a TEM diagram of the catalyst prepared in example 1, b is an enlarged diagram of a, and c is a metal nanoparticle particle size distribution analysis diagram of the catalyst prepared in example 1;

fig. 7 is a TEM image of the catalyst prepared in comparative example 3.

Referring to fig. 2 to 4, metal nanoparticles having a particle size of about 4nm are uniformly dispersed in the pore channels and cage structures of the zeolite of the catalysts prepared in examples 1 to 3.

Referring to fig. 5, metal nanoparticles having a particle size of about 2.7nm are uniformly dispersed in the pores and the cage-like structures of the zeolite of the catalyst prepared in comparative example 1.

Referring to fig. 6, the catalyst prepared in comparative example 2 has metal nanoparticles supported on the surface of silica, and the particle size of the metal nanoparticles is about 3.1 nm.

Referring to fig. 7, the catalyst prepared in comparative example 3 was free of active metal, and the zeolite was free of metal nanoparticles in the pore channels and cage structure.

Comparing fig. 2 to fig. 4 and fig. 7, it can be seen that in the encapsulated zeolite catalyst prepared by the present application, the doping metal is dispersed in the zeolite framework, and the active metal is dispersed in the zeolite pore channels and cage structure.

Effect example 2:

glycerol oxidation experiments were performed using the catalysts prepared in examples 1 to 3 and comparative examples 1 to 3, and the specific experimental procedure is as follows:

before the reaction, the catalyst was pretreated for 2 hours in flowing air (50 mL/min) at 400℃and then sandwiched between the reactors using 500mg of quartz wool for preparing the catalyst bed.

Introducing 0.1mol/L glycerin into the reactor at a mass flow rate of 0.1g/min, introducing air into the reactor at a mass space velocity WHSV of 0.111h at 20mL/min ^-1 The reaction temperature was controlled to 60℃and the type of the reaction-completed product was examined to obtain FIG. 8.

Referring to fig. 8, fig. 8 is a graph showing mass ratio of experimental reaction products of effect example 2 of the present application, in which DHA is 1, 3-dihydroxyacetone, LA is lactic acid, GLD is glyceraldehyde, and GLA is glyceric acid.

As shown in fig. 8, the DHA ratio in the reaction products of the catalysts of examples 1 to 3 was far from that of comparative examples 1 to 3; wherein, the DHA ratio in the reaction product of the catalyst of example 1 reaches 72.2%, the optimal DHA selectivity is obtained, the Sn content of the catalysts of examples 2 and 3 is gradually increased relative to that of example 1, and the DHA ratio in the reaction product is respectively reduced to 57.6% and 57.5%.

The ratio of DHA in the reaction product of the catalyst of comparative example 1 is only less than 30%, and the amount of GLA in the product is far higher than DHA, mainly because the catalyst of comparative example 1 is not added with doped metal Sn, and the single Pt catalyst is mainly used for oxidizing the primary hydroxyl groups of glycerol to generate GLA; similarly, the GLA ratio in the reaction product of the catalyst of comparative example 2 was also much higher than that of the other types, also because comparative example 2 was a single Pt catalyst, while the GLA ratio of comparative example 2 was also lower than that of comparative example 1.

The catalyst of comparative example 3 has little activity in catalyzing the oxidation of glycerol, which suggests that the doping metal Sn itself has no catalytic properties for the oxidation of glycerol molecules and Pt has a critical effect on the activation of glycerol molecules.

Further, as a result of comparing the ratio of the reaction products of examples 1 and comparative examples 1 to 3, the ratio of DHA in the reaction products of comparative examples 1 to 2 is much lower than that of example 1, and the ratio of DHA in the reaction products of comparative example 1 to 2 is no catalytic activity, as compared with the raw material of example 1, the ratio of tin chloride to the raw material of example 1 is small, the ratio of single Pt catalyst to the raw material of comparative example 2 is small, and the ratio of platinum chloride to the raw material of example 1 is small.

It follows that the tin metal of example 1 is used to achieve selective catalytic oxidation of glycerol to DHA by increasing the synergy of the platinum metal and the zeolite, and is not itself catalytically active. The doped metal is dispersed in the framework of the zeolite, so that the synergistic effect of the zeolite and the active metal is greatly enhanced, and the conversion rate of glycerin and the selectivity of DHA are improved.

Effect example 3: analysis of the influence of the Mass space velocity on the catalytic reaction

The catalyst of example 1 was used in the glycerol oxidation test of effect example 2, and the mass space velocities in the test were adjusted to 0.055, 0.111, 0.165 and 0.211h, respectively ^-1 The effect of mass space velocity on the experimental results was analyzed, resulting in fig. 9.

Referring to fig. 9, fig. 9 is a graph showing the mass ratio of the experimental reaction products of effect example 3 of the present application. As shown in fig. 9, the conversion of glycerol decreases with increasing mass space velocity, and the selectivity of DHA is essentially unchanged.

Effect example 4: analysis of the influence of reaction temperature on catalytic reactions

The reaction temperatures in the experiments were adjusted to 60, 80, 100, 120 ℃ respectively using the catalyst of example 1 and the glycerol oxidation experiment of effect example 2, and the influence of the reaction temperatures on the experimental results was analyzed to obtain fig. 10.

Referring to fig. 10, fig. 10 is a graph showing the mass ratio of the experimental reaction products of effect example 4 of the present application. As shown in fig. 10, the glycerol conversion was significantly increased with an increase in the reaction temperature, but the selectivity of DHA was decreased due to an increase in the side reaction.

Effect example 5: long-term test

The catalyst of example 1 was used to conduct a long-term test of 200 hours using the glycerol oxidation test of effect example 2, and the DHA ratio and the glycerol conversion rate in the reaction product were continuously tested, to obtain FIG. 11.

Referring to fig. 11, fig. 11 is a graph showing the mass ratio of the experimental reaction products of effect example 5 of the present application. As shown in fig. 11, the selectivity of DHA was not significantly reduced in the 200h long-term test, kept at 75±2%, and the glycerol conversion was reduced by only 3%, which is probably due to the strong adsorption of the toxic intermediate GLD on the Pt nanoparticle surface.

Therefore, the catalyst of example 1 was found to have excellent catalytic stability.

The previous description of the disclosure is provided to enable any person skilled in the art to make or use the disclosure. Various modifications to the disclosure will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other variations without departing from the scope of the disclosure. Thus, the disclosure is not limited to the examples and designs described herein but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An encapsulated metal zeolite catalyst comprising:

a zeolite;

doping metal, doping and dispersing in the framework of the zeolite;

active metal distributed in the pore canal and cage structure of the zeolite;

2. The encapsulated metal zeolite catalyst of claim 1, wherein the doping metal comprises one or more combinations of Sn, al, mn, sb, the doping metal content of the encapsulated metal zeolite catalyst being 0.01-4.0 wt%;

preferably, the doping metal is Sn.

3. The encapsulated metal zeolite catalyst of claim 1, wherein the active metal comprises one or more combinations of Ru, pd, au, pt, the encapsulated metal zeolite catalyst having a content of the active metal component of 0.01 to 5.0wt%;

preferably, the active metal includes one of Pt, au, pd.

4. The encapsulated metal zeolite catalyst of claim 1 wherein the active metal nanoparticles have a particle size of from 3.0 to 5.5nm.

5. The encapsulated metal zeolite catalyst of claim 1, wherein the zeolite is in the form of ZSM-5, beta, FAU, SSZ-13, MOR or MWW and has a specific surface area of 150 to 300m ² Per gram, the pore volume of the pore canal of the zeolite is 0.07-0.15 cm ³ /g。

6. A process for preparing the encapsulated metal zeolite catalyst as claimed in any one of claims 1 to 5, comprising:

7. The method of claim 6, wherein the organic amine comprises one or more of ammonia, ethylenediamine, n-propylamine, t-butylamine, and trimethylamine, the molar ratio of the organic amine to the active metal salt precursor is (1-600): 1, and the molar ratio of the doped metal salt precursor to the active metal salt precursor is (0.1-5): 1, a step of;

preferably, the molar ratio of the organic amine to the active metal salt precursor is (20-200) to 1;

8. the method of claim 7, wherein the zeolite synthesis mother liquor comprises a template comprising one or more combinations of tetrapropylammonium hydroxide, isopropylamine, di-N-propylamine, N-trimethylsteel alkyl ammonium hydroxide, triethylamine, morpholine and a silicon source comprising one or more combinations of ethyl orthosilicate, sodium silicate, water glass, silica gel; the molar ratio of the active metal salt precursor to the silicon source is (0.0005-0.2) to 1;

preferably, the molar ratio of the active metal salt precursor to the silicon source is (0.001-0.05) to 1;

9. The method according to claim 7, wherein the step of mixing the complex active metal salt solution, the complex doped metal salt solution and the zeolite synthesis mother liquor, evaporating to obtain a reaction gel, and performing a hydrothermal reaction on the reaction gel to obtain a catalyst precursor, wherein the hydrothermal reaction temperature is 120-300 ℃ and the reaction time is 1-20 h;

10. The method according to claim 7, wherein in the step of sequentially centrifugally washing, drying and high-temperature roasting the catalyst precursor, the centrifugally washed detergent comprises one or more of water, acetone and ethanol, and the high-temperature roasting is specifically carried out in an air atmosphere at a temperature rising rate of 1-5 ℃/min to 400-700 ℃ for 1-12 h;

11. Use of the encapsulated metal zeolite catalyst according to any one of claims 1 to 5 or the encapsulated metal zeolite catalyst prepared by the preparation method according to any one of claims 6 to 10 in the preparation of dihydroxyacetone by catalytic selective oxidation of glycerol.