CN114653370A

CN114653370A - Metal oxide based metal monatomic catalyst and preparation method and application thereof

Info

Publication number: CN114653370A
Application number: CN202210172896.6A
Authority: CN
Inventors: 葛晗东; 凌雨轩; 殷雄; 汪乐余
Original assignee: Beijing University of Chemical Technology
Current assignee: Beijing University of Chemical Technology
Priority date: 2022-02-24
Filing date: 2022-02-24
Publication date: 2022-06-24
Anticipated expiration: 2042-02-24
Also published as: CN114653370B

Abstract

The invention providesA metal oxide based metal monatomic catalyst, a method for preparing the same and applications thereof are provided. The metal oxide-based metal monatomic catalyst includes: metal oxide, which is the morphology of mesoporous hollow nanospheres, and metal, which is loaded on the metal oxide in a monoatomic form. When the catalyst is prepared, SiO is used₂Is taken as a template, and utilizes the synergistic effect of the ion exchange process assisted by NaOH and the space confinement effect of the inert outer layer to ensure that metal is not easy to agglomerate in the calcining process, thereby synthesizing ZrO with the mesoporous hollow nanosphere structure₂And TiO₂A metal monoatomic catalyst. The catalyst obtained by the invention can be used for preparing phenylpropyl aldehyde by catalytic hydrogenation of cinnamaldehyde, and has the advantages of low cost, high activity, high selectivity and good cycle stability.

Description

Metal oxide based metal monatomic catalyst, preparation method and application thereof

Technical Field

The invention relates to the technical field of monatomic catalysts, in particular to a metal oxide-based monatomic catalyst, a preparation method thereof and application thereof in catalytic hydrogenation, especially in catalytic hydrogenation of cinnamaldehyde.

Background

The monatomic catalyst is a novel heterogeneous catalyst and is mainly characterized in that a single metal atom is fixed by a coordination element of a surrounding carrier to form a monatomic active site. In order to ensure the atomic-scale dispersion of the single metal atom and avoid the formation of nanoparticles due to aggregation, strong coordination or anchoring action between the single metal atom and the carrier is required, so that the single metal atom in the single-atom catalyst has unique geometric configuration, electronic structure and electronic characteristics.

Compared with the traditional nano catalyst, the monatomic catalyst has the following advantages: the metal dispersity and the atom utilization rate are improved to the maximum extent, and the catalytic activity of the monatomic catalyst is remarkably improved due to the unique electronic structure and the fully exposed active sites of the monatomic catalyst; meanwhile, the monatomic catalyst has highly dispersed active sites and a special geometric configuration, is similar to a homogeneous catalyst, and has sufficient interaction and mass transfer with substrate molecules in space, so that the catalytic selectivity is improved. In addition, the spatial dispersion of the monometallic active sites over the catalyst can also be effective in suppressing side reactions occurring at the multimetallic sites.

At present, the preparation of the monatomic catalyst has the following defects: most of the methods involve high temperature treatment, and the metal monoatomic atoms have high surface energy and are easy to agglomerate under the high temperature treatment condition. Therefore, it is often necessary to remove the metal nanoparticles in conjunction with an acid treatment process. On the one hand, the loading capacity of the monatomic catalyst is far lower than the input amount of the metal precursor, which is not in accordance with the design concept of the monatomic catalyst; on the other hand, the acid treatment process cannot ensure that the quantity of the nanoparticles removed each time is the same, so that the loading capacity of the monatomic catalyst is greatly different even under the same metal input amount, and the control preparation of the monatomic catalyst is not facilitated; finally, the appearance and microstructure of the carrier in the monatomic catalyst can be damaged to a certain extent in the acid treatment process, and the stability of the catalyst is influenced to a certain extent. Therefore, there is a strong need for a universal and efficient method that avoids the agglomeration of single atoms at high temperatures and allows the controlled synthesis of stable metal single atom catalysts.

In view of the above, the present invention is particularly proposed.

Disclosure of Invention

An object of the present invention is to provide a metal oxide-based metal monatomic catalyst.

The second purpose of the invention is to provide a preparation method of the metal oxide based metal monatomic catalyst.

The invention also aims to provide an application of the metal oxide-based metal monatomic catalyst in catalytic hydrogenation (especially cinnamaldehyde catalytic hydrogenation) reaction.

In order to achieve the above purpose of the present invention, the following technical solutions are adopted:

in one aspect, the present invention provides a metal oxide-based metal monatomic catalyst, which comprises: metal oxide, which is the morphology of mesoporous hollow nanospheres, and metal, which is loaded on the metal oxide in a monoatomic form.

The metal oxide may be a support material known in the art for supporting the active components of the catalyst, including but not limited toTiO₂、ZrO₂And the like.

The size of the metal oxide mesoporous hollow nanospheres is not particularly limited, and the metal oxide mesoporous hollow nanospheres can be prepared by selecting a proper method and conditions according to the size required by the application field. In some embodiments, the diameter of the metal oxide mesoporous hollow nanosphere can be 50-1000nm, such as 70-500nm, 110-300nm, 200-240nm, etc., but is not limited thereto. The thickness of the metal oxide mesoporous hollow nanosphere is not particularly limited, and the metal oxide mesoporous hollow nanosphere can be prepared by selecting a suitable method and conditions according to the size required by the application field, and can be 5-50nm, such as 10-50nm, 20-40nm, and the like, but is not limited thereto.

The metal may be a metal element known in the art for use as an active component of a catalyst, including, but not limited to, transition metal elements of the fourth, fifth, and sixth periods of the periodic table, such as Fe, Ni, Cu, Co, Ag, Pt, Pd, and the like.

The metal oxide in the catalyst has a unique hollow mesoporous structure, and the metal is in a monoatomic dispersion state on the metal oxide carrier.

In some embodiments, the loading of metal monoatomic amounts to within 3.0 wt.%, preferably 0.05 to 2.8 wt.%, for example 0.1 to 2.5 wt.%, based on the total weight of the catalyst. Too high a loading of the metal monoatomic species may cause agglomeration, resulting in a decrease in catalytic ability, while too low a loading may result in insufficient catalytic ability.

Further, in some embodiments, the metal is Ni, wherein the Ni monoatomic loading is within 0.5 wt%, preferably 0.05 to 0.45 wt%, for example 0.1 to 0.4 wt%, based on the total weight of the catalyst.

In some embodiments, the metal is Cu, wherein the Cu monatomic loading is within 1.6 wt%, preferably 0.05 to 1.5 wt%, for example 0.1 to 1.4 wt%, based on the total weight of the catalyst.

In some embodiments, the metal is Fe, wherein the Fe monatomic loading is within 2.3 wt%, preferably 0.05 to 2.2 wt%, for example 0.1 to 2.1 wt%, based on the total weight of the catalyst.

The metal monoatomic loading refers to the mass percentage of a monoatomic metal relative to the total weight of the catalyst, that is, the metal monoatomic loading is the mass of the monoatomic metal/mass of the catalyst × 100%.

The metal oxide-based metal monatomic catalyst of the present invention is composed mainly of a metal monatomic and a metal oxide (e.g., M)₁/TiO₂Or M₁/ZrO₂) Composition, but some other impurities may also be present, such as template material or some metal ions that are not removed during the preparation process.

In another aspect, the present invention provides a method for preparing a metal oxide-based metal monatomic catalyst, comprising the steps of:

(1) in SiO₂Depositing a metal oxide layer on the surfaces of the nanospheres to form a material A;

(2) treating the material A in the step (1) with an aqueous solution of alkali metal hydroxide to obtain a material B introduced with alkali metal ions;

(3) treating the material B in the step (2) with a metal salt aqueous solution to obtain a material C introduced with metal ions;

(4) depositing SiO on the surface of the material C in the step (3)₂A template material layer to obtain a material D;

(5) calcining the material D in an inert atmosphere to obtain a material E;

(6) removal of SiO in Material E₂Nanospheres and SiO₂And (3) preparing a template material layer to obtain the metal oxide based metal monatomic catalyst with the mesoporous hollow nanosphere structure.

The method for preparing the metal oxide-based metal monatomic catalyst can effectively avoid the generation of metal nanoparticles, and has the advantages of low cost, good reproducibility and good universality.

Step (1)

In this step, in SiO₂And depositing a metal oxide layer forming material A on the surfaces of the nanospheres.

To SiO₂The source of the nanospheres is not particularly limited. SiO 2₂The nanospheres may be commercially available products or may be prepared by precipitation, hydrothermal synthesis, sol-gel method (

Method) is performed.

The method is carried out by adding tetraethoxysilane, water and ammonia water in turn into a system with ethanol as solvent at normal temperature.

SiO₂The nanospheres are eventually removed as templates and thus their size substantially determines the hollow core size of the finally prepared metal oxide-based metal monatomic catalyst.

To SiO₂The size of the nanosphere is not particularly limited, and SiO with corresponding size can be obtained by purchasing or selecting proper method and conditions according to the size required by the application field₂Nanospheres. In some embodiments, the SiO₂The diameter of the nanoparticle template may be 40-900nm, such as 60-500nm, 100-400nm, etc., but is not limited thereto.

The description of the metal oxide is the same as that of the foregoing, and is not repeated herein.

In a preferred embodiment, the metal oxide is TiO₂Or ZrO₂。

In some embodiments, the reaction is carried out on SiO by a sol-gel reaction₂Depositing a layer of metal oxide, e.g. TiO, on the nanospheres₂Or ZrO₂And (3) a layer. Specifically, step (2) is performed as follows:

in SiO₂In the presence of the nanospheres, a sol-gel reaction is carried out with a metal oxide source (e.g., a titanium source or a zirconium source) as a precursor.

The sol-gel reaction of the metal oxide source may be carried out according to conventional methods in the art. For example, the sol-gel reaction may be carried out in a solvent. The solvent may be a solvent known in the art for preparing metal oxide nanoparticles by a sol-gel reaction. Those skilled in the art can appropriately select the metal oxide source, the surfactant, and the like according to the use. For example, the solvent may be an alcohol compound such as ethanol and isopropanol. In addition, small amounts of water may also be added to the solvent to adjust the rate of hydrolysis and thus the morphology of the metal oxide layer produced. In particular, the solvent may be ethanol, and the volume ratio of ethanol to water may be 10: 1-100: 1.

in addition, a catalyst, such as a base (e.g., aqueous ammonia), may also be added to the sol-gel reaction.

In addition, the sol-gel reaction may be performed in the presence of a stabilizer (e.g., hydroxypropylcellulose) to keep the nanoparticles stable.

The titanium source includes, but is not limited to, TBOT (tetrabutyl titanate), titanium isopropoxide.

The zirconium source includes, but is not limited to, ZBOT (tetrabutyl zirconate), zirconium isopropoxide.

In step (2), the material may be SiO₂Nanosphere template surface deposition of metal oxides (e.g., TiO)₂Or ZrO₂) Layer of a material A, the material A being SiO₂Nanosphere template @ metal oxide (e.g., SiO)₂@TiO₂Or SiO₂@ZrO₂) A nanocomposite material.

The thickness of the metal oxide layer is not particularly limited, and can be prepared by selecting an appropriate method and conditions according to the size required in the application field, and for example, may be 5 to 50nm, such as 10 to 50nm, 20 to 40nm, and the like, but is not limited thereto. For example, the metal oxide (e.g., TiO) formed can be tailored by controlling the amount of metal oxide source (e.g., titanium source or zirconium source) added₂Or ZrO₂) The thickness of the layer.

Step (2)

In this step, the material a obtained in step (2) is treated with an aqueous alkali metal hydroxide solution (e.g., an aqueous NaOH, KOH solution) to obtain a material B into which alkali metal ions are introduced.

Under the action of the aqueous alkali metal hydroxide solution, part of the metal in the metal oxide prepared in the step (1) is replaced by the alkali metal (for example, part of Ti is replaced by Na, and Na is inserted into TiO by replacing Ti sites₂In (b), thereby obtaining a metal oxide-alkali metal (e.g., TiO)_XAlkali metal) to provide a subsequent stepThe site of ion exchange.

In some embodiments, the molar ratio of alkali metal hydroxide added in step (2) to metal oxide source (titanium source or zirconium source) added in step (1) may be 1: 1-16: 1 (e.g. 1: 1, 2: 1, 3: 1, 4: 1, 5: 1, 6: 1, 8: 1, 10: 1, 12: 1, 14: 1, 14.2: 1, 15: 1, 15.2: 1, 16: 1), preferably 1: 1-15: 1, too small a molar ratio of the two, may result in NaOH not sufficiently destroying amorphous (non-crystal structure-forming) metal oxides (e.g., TiO)₂) So that sufficient ion exchange sites cannot be generated, and if the ratio is too large, the morphology of the hollow nanospheres can be seriously affected.

In some embodiments, the treatment time of material a with the aqueous alkali metal hydroxide solution may be 1 to 6 hours.

In step (2), by substituting a part of the metal (e.g., TiO) in the metal oxide with an alkali metal ion₂Part of Ti or ZrO₂Part of Zr) in the above-mentioned alloy, forming a material B which is SiO₂Nanosphere templates @ metal oxides-alkali metal ions (e.g. SiO)₂@TiO₂-Na⁺Or SiO₂@ZrO₂-Na⁺) A nanocomposite material.

In some embodiments, step (2) is performed as follows:

to the aqueous dispersion of material a, an aqueous NaOH solution was added for treatment, followed by solid-liquid separation.

The solid-liquid separation can be carried out by centrifugation. The centrifugation speed is not particularly limited as long as the NaOH aqueous solution can be separated from the solid material as much as possible, and may be, for example, 8000rpm, but is not limited thereto.

Further, the step (2) may further include a step of washing the solid material with water after the solid-liquid separation. The washing method is not particularly limited, and any suitable manner in the art may be employed.

Step (3)

In this step, the material B introduced with alkali metal ions is treated with an aqueous solution of a metal salt so that the metal ions of the metal salt undergo cation exchange with the alkali metal ions previously substituted into the metal oxide, to obtain a material C introduced with metal ions.

The metal of the metal salt may be a metal element known in the art to be used as an active component of the catalyst, including, but not limited to, transition metal elements of the fourth, fifth, and sixth periods of the periodic table, such as Fe, Ni, Cu, Co, Ag, Pt, Pd, and the like. The metal salt may be a water soluble salt of the metal, such as a nitrate, sulphate, hydrochloride.

In some embodiments, the molar ratio of alkali metal hydroxide added in step (2) to metal salt added in step (3) is 0.8: 1-20: 1 (e.g. 1: 1, 2: 1, 3: 1, 4: 1, 5: 1, 6: 1, 8: 1, 10: 1, 12: 1, 14: 1, 15: 1, 16: 1, 18: 1, 20: 1), preferably 1: 1-15: 1.

in some embodiments, the reaction time for treatment with the aqueous metal salt solution may be 12 to 24 hours.

In some embodiments, step (3) is performed as follows: and adding a metal nitrate aqueous solution into the aqueous dispersion of the material B for reaction to obtain a material C.

Thereby, the metal ion of the metal salt is introduced into the metal oxide (e.g., TiO)₂Or ZrO₂) In (b), a material C is obtained, which is a composite material, denoted SiO₂Nanosphere template @ metal oxide-Mⁿ⁺(e.g. SiO)₂@TiO₂-Mⁿ⁺Or SiO₂@ZrO₂-Mⁿ⁺) Wherein, M isⁿ⁺Represents a metal ion, wherein n represents the valence of the metal ion, which is not particularly limited, and may be 1, 2 or 3, such as Fe²⁺、Fe³⁺、Ni²⁺、Cu²⁺、Co²⁺、Ag⁺、Pt²⁺、Pd²⁺。

Step (4)

In this step, the material C (i.e., SiO) obtained in step (3)₂Nanosphere template @ metal oxide-Mⁿ⁺) Surface deposition of SiO₂A layer of template material to obtain material D, i.e. SiO₂Nanosphere template @ metal oxide-Mⁿ⁺@SiO₂Layer of template material (e.g. SiO)₂@TiO₂-Mⁿ⁺@SiO₂Or SiO₂@ZrO₂-Mⁿ⁺@SiO₂)。

By controlling the reaction conditions, e.g. SiO₂The amount of the precursor, the reaction temperature, the reaction time and the like to control SiO₂The thickness of the layer of template material. SiO 2₂The thickness of the layer of template material may typically be in the range of 5-500nm, for example 5-50nm, such as 10-50nm, 20-40nm, etc.

Furthermore, SiO is deposited₂The layer of templating material may be performed in the presence of a stabilizer, such as polyvinylpyrrolidone (PVP), to keep the nanoparticles stable.

In some embodiments, step (4) is performed as follows:

(4.1) mixing the material C with PVP in water to obtain a material C with PVP adsorbed on the surface;

(4.2) SiO in the Presence of Material C having PVP adsorbed on the surface₂Sol-gel reaction of the precursor to deposit SiO on the surface of the material C with PVP adsorbed on the surface₂A layer of template material.

SiO₂The sol-gel reaction of the precursor may be performed according to a conventional method in the art. SiO 2₂The precursor may be SiO conventionally selected in the art₂The precursor is not particularly limited, and may be, for example, an alkoxysilane such as tetraethoxysilane.

In addition, a catalyst such as a base (e.g., ammonia) or the like may be added to the sol-gel reaction.

For example, in some embodiments, the deposition of SiO on the surface of the material C may be achieved by sequentially adding water, tetraethoxysilane and ammonia water to the material C having PVP adsorbed on the surface thereof in a system using ethanol as a solvent to perform a sol-gel reaction₂A layer of template material.

Preferably, the molar ratio of the metal oxide source added in step (1) to the PVP added here may be 70: 1-700: 1.

step (4) may further comprise depositing SiO₂The material behind the template material layer is subjected to solid-liquid separationAnd (5) separating to obtain a solid, and drying the solid. There is no particular limitation on the drying method as long as it is suitable for preparing the catalyst. For example, vacuum drying, spray drying, etc. may be mentioned, but are not limited thereto.

Step (5)

In this step, the material D is calcined under an inert atmosphere to obtain the material E, SiO₂Nano-ball template @ metal oxide-M₁@SiO₂Layer of template material (e.g. SiO)₂@TiO₂-M₁@SiO₂Or SiO₂@ZrO₂-M₁@SiO₂) A nanocomposite material. Wherein M is₁Represents a metal single atom.

The inert gas atmosphere may specifically be a nitrogen gas atmosphere or an argon gas atmosphere. The calcining temperature is 600-900 ℃, the heating rate is 1-5 ℃/min, and the calcining time is 1-3 hours. The metal ion M may be formed by calcination under an inert atmosphereⁿ⁺Conversion to metal monoatomic M₁。

Step (6)

In this step, SiO in the material E is removed₂Nanosphere templates and SiO₂Template material layer to obtain metal oxide-based metal monatomic catalyst with mesoporous hollow nanosphere structure, namely metal oxide-M₁(e.g., TiO)₂-M₁Or ZrO₂-M₁) Monatomic catalyst (sometimes also written as M)₁Metal oxides, e.g. M₁/TiO₂Or M₁/ZrO₂)。

For example, SiO₂Nanosphere templates and SiO₂The layer of template material may be removed by full etching of the template material. The etchant may be any known in the art that can etch SiO₂Including but not limited to aqueous NaOH.

In some embodiments, the etchant NaOH is mixed with the SiO added in step (4)₂The molar ratio of the precursors (e.g., tetraethoxysilane) may be 1.5 to 3. The etching temperature is not particularly limited and may be, for example, 30 to 120 ℃.

Without being bound by any theory, the inventors believe that in the preparation process of the present invention, a part of the metal element of the metal oxide (e.g., TiO) is reacted with an alkali metal hydroxide (e.g., NaOH)₂Ti in (1) with alkali metal ions (e.g. Na)⁺) By substitution to form metal oxide-alkali metal ions (e.g. TiO)_X-Na⁺) The structure of (1), the metal ion being associated with an alkali metal ion (e.g., Na) after addition of the metal salt⁺) Ion exchange takes place in cooperation with the SiO of the outer layer₂The space confinement effect of the template material layer is used for avoiding the agglomeration of metal atoms in the calcining process, and the metal oxide base (such as ZrO) with the mesoporous hollow nano-sphere structure is synthesized₂And TiO₂Group) metal monatomic catalyst. Thus, in the present invention, the outer SiO layer is co-ordinated by an alkali metal hydroxide (e.g. NaOH) assisted ion exchange process₂The steric confinement of the template material, i.e. the immobilization of the metal atoms on the Ti or Zr sites by the ion exchange process on the one hand and the outer coating of SiO on the other hand₂The metal atoms are confined in a limited space, and the metal atoms are not easy to move and agglomerate in the high-temperature calcination process under the synergistic action of the metal atoms and the limited space.

The metal oxide-based metal monatomic catalyst of the invention is mainly composed of a metal monatomic M₁And metal oxides, but some other substances may also be present, e.g. unremoved SiO₂Or a portion of the metal ions.

In some embodiments, the metal oxide is TiO₂Or ZrO₂The metal is selected from transition metal elements in the fourth, fifth and sixth periods of the periodic table, such as Fe, Ni, Cu, Co and the like, and the method for preparing the metal-oxide-based metal monatomic catalyst comprises the following steps:

(1) in SiO₂Deposition of TiO on the surface of nanospheres₂Or ZrO₂Layer (b): in SiO₂Adding a titanium source or a zirconium source into an ethanol water solution in the presence of nanospheres and hydroxypropyl cellulose to perform sol-gel reaction to obtain SiO₂@TiO₂Or SiO₂@ZrO₂；

(2) Treatment of SiO with aqueous NaOH solution₂@TiO₂Or SiO₂@ZrO₂To obtain SiO₂@TiO₂-Na⁺Or SiO₂@ZrO₂-Na⁺(ii) a Wherein the molar ratio of NaOH to the titanium source or the zirconium source is 1: 1-16: 1;

(3) treatment of SiO with aqueous solutions of metal salts₂@TiO₂-Na⁺Or SiO₂@ZrO₂-Na⁺To obtain SiO₂@TiO₂-Mⁿ⁺Or SiO₂@ZrO₂-Mⁿ⁺(ii) a Wherein the molar ratio of NaOH to metal salt is 0.8: 1-20: 1;

(4) mixing SiO₂@TiO₂-Mⁿ⁺Or SiO₂@ZrO₂-Mⁿ⁺Adsorbing PVP on the surface, and then adsorbing SiO with PVP on the surface₂@TiO₂-Mⁿ⁺Or SiO₂@ZrO₂-Mⁿ⁺SiO in the presence of₂Sol-gel reaction of the precursor to obtain SiO₂@TiO₂-Mⁿ⁺@SiO₂Or SiO₂@ZrO₂-Mⁿ⁺@SiO₂；

(5) Mixing SiO₂@TiO₂-Mⁿ⁺@SiO₂Or SiO₂@ZrO₂-Mⁿ⁺@SiO₂Calcining under inert atmosphere to obtain SiO₂@TiO₂-M₁@SiO₂Or SiO₂@ZrO₂-M₁@SiO₂；

(6) SiO removal with aqueous NaOH solution₂@TiO₂-M₁@SiO₂Or SiO₂@ZrO₂-M₁@SiO₂SiO in (2)₂To obtain TiO₂-M₁Or ZrO₂-M₁Monatomic catalyst (sometimes also referred to as M)₁/TiO₂Or M₁/ZrO₂)。

The invention also provides the metal oxide-based metal monatomic catalyst prepared by the method. In some embodiments, the metal-oxide-based metal monatomic catalyst is described in the same manner as described above and will not be described in detail herein.

According to the catalytic activity of the metal, the catalyst of the invention can be applied to different fields, such as thermocatalytic hydrogenation, thermocatalytic oxidation, electrocatalysis, photocatalysis, quasi-nanoenzyme catalysis, photoelectrocatalysis and the like.

In a further aspect, the invention provides the use of a metal oxide-based metal monatomic catalyst according to the invention or prepared according to the method of the invention, in catalytic hydrogenation, in particular in the preparation of phenylpropanal by catalytic hydrogenation of cinnamaldehyde.

The metal oxide-based metal monatomic catalyst can be used in any catalytic hydrogenation and has wide application prospect. Taking catalytic hydrogenation of cinnamaldehyde to prepare phenylpropyl aldehyde as an example, the method has high cinnamaldehyde hydrogenation conversion rate, high phenylpropyl aldehyde selectivity and high cycle stability.

In a preferred embodiment, the method for selectively hydrogenating cinnamaldehyde according to the present invention comprises the steps of: cinnamaldehyde is subjected to a hydrogenation reaction in the presence of a metal oxide-based monatomic catalyst according to the present invention or a metal oxide-based monatomic catalyst prepared according to the method of the present invention. The method has high cinnamaldehyde hydrogenation conversion rate and phenylpropyl aldehyde selectivity, and high cycle stability.

In the above-mentioned method, the temperature, time and pressure of the reaction may be conventional reaction conditions for hydrogenation reaction without particular limitation. For example, the reaction temperature may be 90 to 140 deg.C (e.g., 100, 120, 130 deg.C), the reaction time may be 1 to 3 hours, and the reaction pressure may be 0.4 to 4 MPa.

Advantageous effects

(1) The catalyst metal is loaded on the metal oxide in a monatomic form, has a unique hollow mesoporous structure, can provide more active sites per unit mass, reduces diffusion resistance, can be used in catalytic hydrogenation reaction, particularly for preparing phenylpropyl aldehyde by catalytic hydrogenation of cinnamyl aldehyde, has higher cinnamyl aldehyde hydrogenation conversion rate and phenylpropyl aldehyde selectivity, and has high cycle stability.

(2) The invention prepares the catalyst with SiO₂As a template, and using NaOH-assisted ion exchange process with an inert outer layer(SiO₂Template layer) of the space confinement effect (on the one hand fixing metal atoms to Ti or Zr sites by an ion exchange process and on the other hand coating SiO with an outer layer₂Metal atoms are confined in a limited space and are synergistic with each other), so that the metal is not easy to agglomerate in the calcining process, an acid treatment process is not needed, and the metal oxide (ZrO) with the mesoporous hollow nanosphere structure is synthesized₂And TiO₂) The catalyst has low cost, high activity, high selectivity and high circulation stability.

(3) The monatomic preparation method can effectively inhibit the generation of metal nanoparticles, avoids the resource waste in the acid treatment process, provides a new thought for the synthesis of the monatomic catalyst, and provides more possibilities for the industrial application of the monatomic catalyst.

(4) The method provided by the invention has wider universality, can be suitable for various metal single atoms, and ensures that the metal load under the single atom can be correspondingly increased or reduced within a certain range.

The present invention has been described in detail hereinabove, but the above embodiments are merely illustrative in nature and are not intended to limit the present invention. Furthermore, there is no intention to be bound by any theory presented in the preceding prior art or the summary or the following examples.

Unless expressly stated otherwise, a numerical range throughout this specification includes any sub-range therein and any numerical value incremented by the smallest sub-unit within a given value. Unless expressly stated otherwise, numerical values throughout this specification represent approximate measures or limitations to the extent that they include minor deviations from the given values, as well as embodiments having values about the mentioned as well as having the precise values mentioned. Other than in the operating examples provided at the end of the detailed description, all numbers expressing quantities or conditions of parameters (e.g., quantities or conditions) used in this specification, including the appended claims, are to be understood as being modified in all instances by the term "about" whether or not "about" actually appears before the number. "about" means that the numerical value so described is susceptible to slight imprecision (with some approach to exactness in that value; approximately or reasonably close to that value; approximately). As used herein, "about" refers to at least variations that can be produced by ordinary methods of measuring and using such parameters, provided that the imprecision provided by "about" is not otherwise understood in the art with this ordinary meaning. For example, "about" can include variations of less than or equal to 10%, less than or equal to 5%, less than or equal to 4%, less than or equal to 3%, less than or equal to 2%, less than or equal to 1%, or less than or equal to 0.5%.

Drawings

FIG. 1 shows Ni produced in example 1 of the present invention₁/TiO₂Electron micrographs of (A).

FIG. 2 shows Ni produced in example 2 of the present invention₁/ZrO₂Electron micrographs of (A).

FIG. 3 shows Ni produced in example 1 of the present invention₁/TiO₂X-ray diffraction pattern of (a).

FIG. 4 shows Ni prepared in example 2 of the present invention₁/ZrO₂X-ray diffraction pattern of (a).

FIG. 5 shows Ni prepared in example 1 of the present invention₁/TiO₂Spherical aberration corrected high angle annular dark field scanning transmission electron microscope (HAADF-STEM) photographs of monatomic catalysts.

FIG. 6 shows Ni prepared in example 2 of the present invention₁/ZrO₂Spherical aberration corrected high angle annular dark field scanning transmission electron microscope (HAADF-STEM) photographs of monatomic catalysts.

Detailed Description

The present invention is further illustrated by the following examples, which are provided for illustrative purposes only and are not to be construed as limiting the scope of the invention.

The starting materials, reagents, methods and the like used in the examples are those conventional in the art unless otherwise specified.

Tetraethoxysilane: alfa Aesar;

n-butyl titanate, n-butyl zirconate: j & K;

inductively coupled plasma spectrometer: model iCAP 6000 series;

transmission electron microscope: model JEOL JEM-1200, the accelerating voltage is 100 KV;

x-ray diffractometer: model Bruker AXS D8-Advanced;

spherical aberration correction transmission electron microscope: the model Titan cube Themis G2300.

Example 1: ni₁/TiO₂Synthesis of

SiO₂The synthesis of (2): 23mL of ethanol was poured into a 50mL Erlenmeyer flask, stirred, then 0.86mL of TEOS was poured, stirred for 3 minutes, and then 4mL of H was poured₂O, stirred for another 3 minutes, and 0.8mL NH was injected₃·H₂And (O). After 4 hours of reaction, the product was finally dispersed in 10mL of ethanol by centrifugation 3 times with ethanol (8000rpm, 5 minutes).

SiO₂@TiO₂The synthesis of (2): firstly, adding 10mL of high-purity ethanol and 7mL of high-purity acetonitrile into a 50mL conical flask, stirring for 3 minutes, adding 50mg of hydroxypropyl cellulose, stirring for 30 minutes, and after the hydroxypropyl cellulose is completely dissolved, adding the SiO synthesized in the previous step₂The mixture was poured into the reaction solution, and after 10 minutes, 0.2mL of NH was poured₃·H₂And O, after 10 minutes, injecting TBOT buffer solution (1mL of TBOT, 3mL of high-purity ethanol (more than or equal to 99.5 percent) and 1mL of high-purity acetonitrile (more than or equal to 99.9 percent)) and after 2 hours of reaction, centrifuging to collect the product (firstly centrifuging with ethanol for 3 times, then centrifuging with water for three times, 8000rpm, and 5 minutes).

SiO₂@TiO₂-Ni²⁺: the reaction mixture was treated with 10. mu.L of 2.5mol/L NaOH, reacted for 30 minutes, centrifuged 2 times with deionized water, the reaction mixture was dispersed in 40mL of deionized water, and then 500. mu.L of 0.05mol/L aqueous nickel nitrate hexahydrate was added, reacted for 12 hours, and centrifuged 3 times with deionized water (8000rpm, 5 minutes).

SiO₂@TiO₂-Ni²⁺@SiO₂The synthesis of (2): first, the sample synthesized in the previous step was dispersed in 20mL of deionized water, and an aqueous solution (M) containing 200mg of PVP was added_w：40000，2mL H₂O) is stirred for 12 hours, so that PVP is fully adsorbed on TiO₂Of (2) is provided. Centrifugally collecting with deionized waterWill not adsorb on TiO₂The PVP on the surface was removed. 8000rpm, 5 minutes); dispersing the sample with PVP adsorbed on the surface in 23mL of ethanol, adding 4.3mL of deionized water, stirring for 3 minutes, adding 0.86mL of TEOS, stirring for 3 minutes, adding 0.8mL of NH₃·H₂O, after 3 hours of reaction, was centrifuged three times with ethanol and the product was collected (8000rpm, 5 minutes) and then dried in a vacuum oven for further use.

High-temperature calcination: grinding the dried sample in the previous step into powder, placing the powder into a porcelain boat, transferring the porcelain boat into a tube furnace, and introducing N₂Removing air in the tube furnace, starting to heat up after 30 minutes, setting the heating rate at 5 ℃/min, keeping at 800 ℃ for 2 hours, and taking out the porcelain boat after naturally cooling to room temperature.

Ni₁/TiO₂The synthesis of (1) dispersing the calcined sample in deionized water, adding sufficient 2.5mol/L NaOH aqueous solution, heating to 90 ℃ in an oil bath, introducing condensed water for reflux, and reacting until SiO is completely removed₂The template was centrifuged through deionized water to remove excess Na⁺Until the pH of the centrifuged supernatant is neutral, drying in a vacuum drying oven at 60 deg.C for 12 hr, taking out, and grinding into powder in a mortar to obtain Ni₁/TiO₂A monatomic catalyst.

Ni measurement by inductively coupled plasma emission spectrometer₁In Ni₁/TiO₂The loading was 0.4 wt%.

Example 2: ni₁/ZrO₂Synthesis of (2)

SiO₂The synthesis of (2): the same as in example 1.

SiO₂@ZrO₂The synthesis of (2): first 20mL of ethanol and 0.1mL of H were added to a 50mL Erlenmeyer flask₂O, stirring for 3 minutes, adding 10mg of hydroxypropyl cellulose, stirring for 10 minutes, and after the hydroxypropyl cellulose is completely dissolved, adding the SiO synthesized in the previous step₂After 20 minutes, a ZBOT buffer solution (0.6mL of ZBOT,4.4mL of ethanol) was injected, and after 20 hours of reaction, the product was collected by centrifugation (2 times with ethanol, 2 times with water,8000rpm, 4 minutes).

SiO₂@ZrO₂-Ni²⁺The synthesis of (2): the reaction mixture was treated with 10. mu.L of 2.5mol/L NaOH, reacted for 30 minutes, centrifuged 2 times with deionized water, the reaction mixture was dispersed in 40mL of deionized water, and then 500. mu.L of 0.05mol/L aqueous nickel nitrate hexahydrate was added, reacted for 12 hours, and centrifuged 3 times with deionized water (8000rpm, 5 minutes).

SiO₂@ZrO₂-Ni²⁺@SiO₂The synthesis of (2): the same as in example 1.

High-temperature calcination: the same as in example 1.

Ni₁/ZrO₂The synthesis of (2): ni was measured by inductively coupled plasma emission spectrometer as in example 1₁In Ni₁/ZrO₂The loading on the catalyst was 0.5 wt%.

Transmission electron microscopy characterization:

FIGS. 1 and 2 show Ni obtained in example 1₁/TiO₂And Ni obtained in example 2₁/ZrO₂In a Transmission Electron Microscope (TEM) photograph of (4), Ni was observed₁/TiO₂And Ni₁/ZrO₂All the shapes of the nano-spheres are hollow nano-spheres. For prepared Ni₁/TiO₂And Ni₁/ZrO₂The electron microscope samples were observed at multiple angles, not in TiO₂And ZrO₂Ni or other nanoparticles were observed on the surface of the support.

And (3) characterization of a spherical aberration electron microscope:

ni prepared separately for examples 1 and 2₁/TiO₂And Ni₁/ZrO₂The characterization was performed by using a spherical aberration electron microscope, as shown in FIGS. 5 and 6. Ni exists in the form of independent and obvious bright points in a spherical aberration electron microscope, and proves that metal Ni is dispersed in TiO in the form of monoatomic atoms₂And ZrO₂In a carrier.

The monoatomic atom exists in a manner of coordinating with O on the metal oxide support.

Characterization by X-ray diffraction:

examples 1 and 2 respectively produce Ni₁/TiO₂And Ni₁/ZrO₂The X-ray diffraction pattern of (A) is shown in FIG. 3And shown in fig. 4. Illustrating TiO₂The crystal phase of (A) is anatase phase, ZrO₂The crystal phase of (2) is a tetragonal phase.

Example 3: fe₁/TiO₂Synthesis of (2)

The other conditions and procedures of this example were the same as those of example 1 except that the nickel nitrate hexahydrate aqueous solution was replaced with an equal concentration of an equal volume of ferric nitrate hexahydrate aqueous solution.

Example 4: fe₁/ZrO₂Synthesis of (2)

The other conditions and procedures of this example were the same as those of example 2 except that the nickel nitrate hexahydrate aqueous solution was replaced with an equal concentration of an equal volume of ferric nitrate hexahydrate aqueous solution.

Example 5: cu₁/TiO₂Synthesis of (2)

The other conditions and procedures of this example were the same as those of example 1 except that the aqueous solution of nickel nitrate hexahydrate was replaced with an equal concentration of an equal volume of aqueous solution of copper nitrate hexahydrate.

Example 6: cu₁/ZrO₂Synthesis of (2)

The conditions and procedures of this example were otherwise the same as those in example 2 except that the aqueous solution of nickel nitrate hexahydrate was replaced with an equal-concentration equal-volume aqueous solution of copper nitrate hexahydrate.

Example 7: co₁/TiO₂Synthesis of (2)

The other conditions and procedures of this example were the same as those of example 1 except that the aqueous solution of nickel nitrate hexahydrate was replaced with an equal-concentration equal-volume aqueous solution of cobalt nitrate hexahydrate.

Example 8: co₁/ZrO₂Synthesis of (2)

The other conditions and procedures of this example were the same as those of example 2 except that the aqueous solution of nickel nitrate hexahydrate was replaced with an equal-concentration equal-volume aqueous solution of cobalt nitrate hexahydrate.

Example 9: ag₁/TiO₂Synthesis of (2)

The other conditions and procedures of this example were the same as those of example 1 except that the aqueous nickel nitrate hexahydrate solution was replaced with an equal concentration of an equal volume of aqueous silver nitrate hexahydrate solution.

Example 10: ag₁/ZrO₂Synthesis of (2)

The other conditions and procedures of this example were the same as those of example 2 except that the aqueous nickel nitrate hexahydrate solution was replaced with an equal concentration of an equal volume of aqueous silver nitrate hexahydrate solution.

Example 11: pt₁/TiO₂Synthesis of (2)

The other conditions and procedures of this example were the same as those of example 1 except that the aqueous solution of nickel nitrate hexahydrate was replaced with an equal-concentration and equal-volume aqueous solution of platinum tetraammine nitrate.

Example 12: pt₁/ZrO₂Synthesis of (2)

The conditions and procedures of this example were otherwise the same as those in example 2, except that the aqueous solution of nickel nitrate hexahydrate was replaced with an equal-concentration equal-volume aqueous solution of platinum tetraammine nitrate.

Example 13: pd₁/TiO₂Synthesis of (2)

The other conditions and procedures of this example were the same as those of example 1 except that the aqueous solution of nickel nitrate hexahydrate was replaced with an equal concentration of an equal volume of aqueous palladium nitrate.

Example 14: pd₁/ZrO₂Synthesis of (2)

The other conditions and procedures of this example were the same as those of example 2 except that the aqueous solution of nickel nitrate hexahydrate was replaced with an equal concentration of an equal volume of aqueous palladium nitrate.

Comparative example 1: ni_nps/TiO₂Synthesis of (2)

The comparative example was conducted under the same conditions and in the same procedure as in example 1 except that the volume of the nickel nitrate hexahydrate aqueous solution was increased by ten times.

Comparative example 2: ni_nps/ZrO₂Synthesis of (2)

The comparative example was conducted under the same conditions and in the same procedure as in example 2 except that the volume of the nickel nitrate hexahydrate aqueous solution was increased by ten times.

Comparative example 3: ni_nps/SiO₂Synthesis of (2)

Using commercial SiO₂Is used as a carrier and is synthesized by a simple impregnation method.

Application example

The catalysts prepared in examples and comparative examples were used in cinnamaldehyde hydrogenation reactions. The specific process is as follows:

adding 25.0mg of catalyst, 50 mu L of reactant cinnamyl aldehyde and 25.0mL of isopropanol into a 100mL reaction kettle lining in sequence, installing the reaction kettle, and firstly filling and discharging H after ensuring that the reaction kettle is completely sealed₂5 times (each time introducing about 1MPa H)₂) Exhausting air in the reaction kettle, and introducing 3MPa H₂The reaction temperature was set at 130 ℃ for 2 hours.

After the reaction is finished, after the high-pressure reaction kettle is cooled to room temperature, the lining is taken out, about 50mg of internal standard substance biphenyl is added, after the biphenyl is completely dissolved, about 2.0mL of solution after the reaction is taken out by using an injector, impurities such as catalyst powder and the like are filtered by using a filter membrane, the solution is diluted by a certain multiple (the concentration of a reactant is ensured to be lower than 100ppm), the diluted solution is injected by a microsyringe, and the content of a product is analyzed by gas chromatography.

The conversion was calculated as follows:

conversion rate:cinnamicaldehyde consumption before and after reaction/cinnamic aldehyde charge amount × 100%;

the selectivity is calculated as follows:

selectivity% (% phenylpropanal) molar amount/total molar amount of cinnamyl alcohol, phenylpropanal and phenylpropanol x 100%.

As shown in table 1, table 2 and table 3, wherein COL represents cinnamyl alcohol, HCAL represents phenylpropanal, and HCOL represents phenylpropanol.

TABLE 1

TABLE 2

TABLE 3

The results show that in the catalyst obtained, Ni₁/TiO₂Shows the most excellent catalytic performance, at 130 ℃, 3MPa H₂Under the reaction condition of 2 hours, the conversion rate of the cinnamaldehyde can reach 98 percent, and the selectivity of the phenylpropyl aldehyde can reach 90 percent.

The above embodiments are only used to illustrate the technical solution of the present invention, and not to limit the same. While the invention has been described in detail and with reference to the foregoing embodiments, it will be understood by those skilled in the art that: modifications may be made to the embodiments described above, or equivalents may be substituted for some or all of the features thereof without departing from the spirit and scope of the invention as defined by the claims; but such modifications or substitutions are intended to be included within the scope of the present invention as defined in the appended claims.

Claims

1. A metal oxide-based metal monatomic catalyst, comprising: metal oxide which is the shape of the mesoporous hollow nanosphere, and metal which is loaded on the metal oxide in a monoatomic form;

preferably, the diameter of the metal oxide mesoporous hollow nanosphere is 50-1000nm, preferably 70-500nm or 110-300nm, and the thickness of the metal oxide mesoporous hollow nanosphere is 5-50nm, preferably 10-50nm or 20-40 nm.

2. The metal-oxide-based metal monatomic catalyst according to claim 1, wherein the metal is selected from transition metal elements of the fourth, fifth and sixth periods of the periodic table, preferably from one or more of Fe, Ni, Cu, Co, Ag, Pt and Pd;

the metal oxide is selected from TiO₂And ZrO₂One or more of the above;

preferably, the loading of metal monoatomic catalyst is within 3.0 wt%, preferably 0.05 to 2.8 wt%, more preferably 0.1 to 2.5 wt%, based on the total weight of the metal oxide-based metal monoatomic catalyst;

preferably, the metal is Ni, and the loading of Ni monoatomic atoms is within 0.5 wt%, preferably 0.05 to 0.45 wt%, more preferably 0.1 to 0.4 wt%, based on the total weight of the metal oxide-based metal monoatomic catalyst; or

The metal is Cu, and the loading amount of Cu single atom is within 1.6 wt%, preferably 0.05-1.5 wt%, and more preferably 0.1-1.4 wt%, based on the total weight of the metal oxide-based metal single atom catalyst; or

The metal is Fe, and the loading amount of Fe monatomic is within 2.3 wt%, preferably 0.05 to 2.2 wt%, more preferably 0.1 to 2.1 wt%, based on the total weight of the metal oxide-based metal monatomic catalyst.

3. A method of preparing a metal oxide-based metal monatomic catalyst, comprising the steps of:

(1) in SiO₂Depositing a metal oxide layer on the surface of the nanosphere to form a material A;

(3) treating the material B obtained in the step (2) with a metal salt aqueous solution to obtain a material C introduced with metal ions;

(5) calcining the material D in an inert atmosphere to obtain a material E;

4. The method of claim 3,

SiO in step (1)₂The diameter of the nanosphere is 40-900nm, preferably 60-500nm or 100-400 nm; and/or

In step (1), in SiO₂In the presence of nanospheres, a sol-gel reaction is carried out by taking a metal oxide source as a precursor, so that SiO is generated₂Depositing a metal oxide layer on the nanospheres;

preferably, the metal oxide source is a titanium source or a zirconium source,

preferably, the titanium source is one or more selected from tetrabutyl titanate and titanium isopropoxide; the zirconium source is one or more selected from tetrabutyl zirconate and zirconium isopropoxide;

preferably, the thickness of the metal oxide layer is 5-50nm, such as 10-50nm or 20-40 nm.

5. The method of claim 3,

in the step (2), the alkali metal hydroxide is selected from one or more of NaOH and KOH, preferably NaOH; and/or

In the step (3), the metal in the metal salt is selected from transition metal elements in the fourth, fifth and sixth periods of the periodic table, preferably one or more selected from Fe, Ni, Cu and Co, and the metal salt is one or more selected from nitrate, sulfate and hydrochloride.

6. The method of claim 4,

the molar ratio of the alkali metal hydroxide added in the step (2) to the metal oxide source added in the step (1) is 1: 1-16: 1; and/or

The molar ratio of the alkali metal hydroxide added in the step (2) to the metal salt added in the step (3) is 0.8: 1-20: 1.

7. the method of claim 3,

the step (4) is carried out as follows:

(4.1) mixing the material C with polyvinylpyrrolidone in water to obtain a material C with polyvinylpyrrolidone adsorbed on the surface;

(4.2) SiO in the Presence of Material C having polyvinylpyrrolidone adsorbed on the surface₂Sol-gel reaction of precursorsDepositing SiO on the surface of the material C with polyvinylpyrrolidone adsorbed on the surface₂A layer of template material; and/or

In the step (5), the inert atmosphere is a nitrogen atmosphere or an argon atmosphere; and/or the calcination temperature is 600-900 ℃; and/or the heating rate is 1-5 ℃/min; and/or the calcination time is 1-3 hours; and/or

In the step (6), SiO in the material E is removed by etching₂Nanospheres and SiO₂The template material layer is etched by NaOH aqueous solution at 30-120 deg.C.

8. A method according to claim 3, characterized by the steps of:

(1) in SiO₂Deposition of TiO on the surface of nanospheres₂Or ZrO₂Layer (b): in SiO₂Adding a titanium source or a zirconium source into an ethanol/water solution in the presence of nanospheres and hydroxypropyl cellulose to perform sol-gel reaction to obtain SiO₂@TiO₂Or SiO₂@ZrO₂；

(4) mixing SiO₂@TiO₂-Mⁿ⁺Or SiO₂@ZrO₂-Mⁿ⁺Adsorbing polyvinylpyrrolidone on the surface, and then adsorbing SiO of polyvinylpyrrolidone on the surface₂@TiO₂-Mⁿ⁺Or SiO₂@ZrO₂-Mⁿ⁺SiO in the presence of₂Sol-gel reaction of the precursor to obtain SiO₂@TiO₂-Mⁿ⁺@SiO₂Or SiO₂@ZrO₂-Mⁿ⁺@SiO₂；

(6) SiO removal with aqueous NaOH solution₂@TiO₂-M₁@SiO₂Or SiO₂@ZrO₂-M₁@SiO₂SiO in (2)₂To obtain TiO₂-M₁Or ZrO₂-M₁A monatomic catalyst.

9. Use of a metal oxide-based metal monatomic catalyst as defined in claim 1 or 2 or as prepared according to the process defined in any one of claims 3 to 8, in catalytic hydrogenation, in particular in the preparation of phenylpropanal by catalytic hydrogenation of cinnamaldehyde.

10. Use according to claim 9, characterized in that it comprises the following steps: subjecting cinnamaldehyde to a hydrogenation reaction in the presence of a metal oxide-based monatomic catalyst according to claim 1 or 2, or a metal oxide-based monatomic catalyst prepared according to the method of any one of claims 3 to 8.