CN114653370B - Metal oxide-based metal monoatomic catalyst, and preparation method and application thereof - Google Patents

Metal oxide-based metal monoatomic catalyst, and preparation method and application thereof Download PDF

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CN114653370B
CN114653370B CN202210172896.6A CN202210172896A CN114653370B CN 114653370 B CN114653370 B CN 114653370B CN 202210172896 A CN202210172896 A CN 202210172896A CN 114653370 B CN114653370 B CN 114653370B
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CN114653370A (en
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葛晗东
凌雨轩
殷雄
汪乐余
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Beijing University of Chemical Technology
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Abstract

The invention provides a metal oxide-based metal monoatomic catalyst, a preparation method and application thereof. The metal oxide-based metal monoatomic catalyst includes: a metal oxide which is the morphology of mesoporous hollow nanospheres, and a metal which is supported on the metal oxide in the form of a single atom. In the preparation of the catalyst, siO is used 2 As a template, and utilizes the synergistic effect of the NaOH-assisted ion exchange process and the space limiting effect of the inert outer layer to ensure that metals are not easy to agglomerate in the calcining process, thereby synthesizing the ZrO with the mesoporous hollow nanosphere structure 2 And TiO 2 A base metal monoatomic catalyst. The catalyst obtained by the invention can be used for preparing benzene propionaldehyde by catalytic hydrogenation of cinnamaldehyde, and has the advantages of low cost, high activity, high selectivity and good cycling stability.

Description

Metal oxide-based metal monoatomic catalyst, and preparation method and application thereof
Technical Field
The invention relates to the technical field of monoatomic catalysts, in particular to a metal oxide-based monoatomic catalyst, a preparation method thereof and application thereof in catalytic hydrogenation, in particular to cinnamaldehyde catalytic hydrogenation reaction.
Background
The single-atom catalyst is a novel heterogeneous catalyst and is mainly characterized in that single metal atoms are fixed by coordination elements of surrounding carriers to form single-atom active sites. In order to ensure the atomic-level dispersion of the individual metal atoms, avoiding the formation of nanoparticles due to aggregation, a strong coordination or anchoring effect between the individual metal atoms and the carrier is required, which leads to the individual metal atoms in the single-atom catalyst having unique geometric configuration, electronic structure and electronic characteristics.
Compared with the traditional nano catalyst, the single-atom catalyst has the following advantages: the metal dispersity and the atom utilization rate are improved to the maximum extent, and the unique electronic structure and fully exposed active sites of the single-atom catalyst obviously improve the catalytic activity; meanwhile, the monoatomic catalyst has highly dispersed active sites and special geometric configuration, is similar to a homogeneous catalyst, and has sufficient interaction and mass transfer effect with substrate molecules in space, so that the selectivity of catalysis is improved. In addition, spatial dispersion of the single metal active sites on the catalyst can also be effective in inhibiting side reactions that occur at the multi-metal sites.
At present, the preparation of monoatomic catalysts has the following disadvantages: most of the methods involve high temperature treatment processes, while metal monoatoms have high surface energy and are extremely prone to agglomeration under high temperature treatment conditions. Therefore, it is often necessary to remove the metal nanoparticles in conjunction with an acid treatment process. On the one hand, the loading of the single-atom catalyst is far lower than the input of the metal precursor, which does not accord with the design concept of the single-atom catalyst; on the other hand, the acid treatment process cannot ensure that the number of the nano particles removed each time is the same, so that the loading amount of the single-atom catalyst is greatly different even under the same metal input amount, and the controllable preparation of the single-atom catalyst is not facilitated; finally, the acid treatment process also damages the morphology and microstructure of the carrier in the monoatomic catalyst to a certain extent, and affects the stability of the catalyst to a certain extent. Therefore, there is an urgent need for a versatile and efficient process that avoids agglomeration of single atoms at high temperatures and allows controlled synthesis of stable metal single atom catalysts.
In view of this, the present invention has been made.
Disclosure of Invention
It is an object of the present invention to provide a metal oxide-based metal monoatomic catalyst.
The second object of the invention is to provide a method for preparing the metal oxide-based metal monoatomic catalyst.
The invention further aims to provide an application of the metal oxide-based metal single-atom catalyst in catalytic hydrogenation (especially cinnamaldehyde catalytic hydrogenation) reaction.
In order to achieve the above object of the present invention, the following technical solutions are specifically adopted:
in one aspect, the present invention provides a metal oxide-based metal monoatomic catalyst comprising: a metal oxide which is the morphology of mesoporous hollow nanospheres, and a metal which is supported on the metal oxide in the form of a single atom.
The metal oxide may be a support material known in the art for supporting the catalyst active component including, but not limited to, tiO 2 、ZrO 2 Etc.
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 metal oxide mesoporous hollow nanospheres may have diameters ranging from 50 to 1000nm, such as 70 to 500nm,110 to 300nm,200 to 240nm, etc., but are not limited thereto. The thickness of the metal oxide mesoporous hollow nanospheres is not particularly limited, and can be prepared by selecting a proper method and conditions according to the size required in the application field, and can be 5-50nm, for example, 10-50nm,20-40nm, etc., but is not limited thereto.
The metal may be a metal element known in the art for use as a catalyst active component, including but not limited to transition metal elements of the fourth, fifth, sixth period of the periodic table, such as Fe, ni, cu, co, ag, pt, pd, etc.
The metal oxide in the catalyst has a unique hollow mesoporous structure, and the metal is in a monoatomic dispersion state on a metal oxide carrier.
In some embodiments, the loading of metal monoatoms is within 3.0wt%, preferably 0.05 to 2.8wt%, for example 0.1 to 2.5wt%, based on the total weight of the catalyst. Too high a loading of metal monoatoms may cause agglomeration, resulting in a decrease in catalytic ability, while too low a loading may cause insufficient catalytic ability.
Further, in some embodiments, the metal is Ni, wherein the Ni monoatomic loading is within 0.5wt%, preferably from 0.05 to 0.45wt%, such as from 0.1 to 0.4wt%, based on the total weight of the catalyst.
In some embodiments, the metal is Cu, wherein the Cu monoatomic loading is within 1.6wt%, preferably 0.05 to 1.5wt%, for example 0.1 to 1.4wt%, based on the total weight of the catalyst.
In some embodiments, the metal is Fe, wherein the Fe monoatomic loading is within 2.3wt%, preferably 0.05 to 2.2wt%, for example 0.1 to 2.1wt%, based on the total weight of the catalyst.
The metal monoatomic loading refers to the mass percent of monoatomic metal relative to the total weight of the catalyst, i.e., metal monoatomic loading = mass of monoatomic metal/mass of catalyst x 100%.
The metal oxide-based metal monoatomic catalyst of the present invention consists essentially of a metal monoatom and a metal oxide (e.g., M 1 /TiO 2 Or M 1 /ZrO 2 ) A composition, but may also have some other impurities, such as template material or some metal ions, which are not removed during the preparation process.
In another aspect, the present invention provides a method for preparing a metal oxide-based metal monoatomic catalyst, comprising the steps of:
(1) In SiO 2 Depositing a metal oxide layer on the surface of the nanosphere to form a material A;
(2) Treating the material A in the step (1) with an alkali metal hydroxide aqueous solution to obtain a material B into which alkali metal ions are introduced;
(3) Treating the material B in the step (2) with an aqueous solution of a metal salt to obtain a material C into which metal ions are introduced;
(4) Depositing SiO on the surface of the material C in the step (3) 2 Die plate material layerObtaining a material D;
(5) Calcining the material D in an inert atmosphere to obtain a material E;
(6) Removal of SiO from material E 2 Nanospheres and SiO 2 And (3) a template material layer to obtain the metal oxide-based metal monoatomic catalyst with the mesoporous hollow nanosphere structure.
The method for preparing the metal oxide-based metal monoatomic catalyst can effectively avoid the generation of metal nano particles, and has the advantages of low cost, good reproducibility and good universality.
Step (1)
In this step, at SiO 2 The metal oxide layer is deposited on the surface of the nanospheres to form a material A.
For SiO 2 The source of the nanospheres is not particularly limited. SiO (SiO) 2 The nanospheres can be commercial products or prepared by precipitation method, hydrothermal synthesis method and sol-gel method
Figure BDA0003519151160000031
Method) synthesis. />
Figure BDA0003519151160000032
The method is to add tetraethoxysilane, water and ammonia water into a system with ethanol as a solvent in sequence, and the process is carried out under the normal temperature condition.
SiO 2 The nanospheres eventually are removed as templates and thus their size essentially determines the hollow size of the finally prepared metal oxide based metal monoatomic catalyst.
For SiO 2 The size of the nanospheres is not particularly limited, and SiO with corresponding size can be prepared by purchasing or selecting proper methods and conditions according to the size required by the application field 2 A nanosphere. In some embodiments, siO 2 The diameter of the nanosphere template may be 40-900nm, for example, 60-500nm,100-400nm, etc., but is not limited thereto.
The description of the metal oxide is the same as that described above, and will not be repeated here.
In a preferred embodiment, the metal oxide is TiO 2 Or ZrO(s) 2 。
In some embodiments, the SiO is formed by a sol-gel reaction 2 Deposition of metal oxide layers, e.g. TiO, on nanospheres 2 Or ZrO(s) 2 A layer. Specifically, step (2) is performed as follows:
in SiO 2 In the presence of nanospheres, a metal oxide source (such as a titanium source or a zirconium source) is used as a precursor to perform sol-gel reaction.
The sol-gel reaction of the metal oxide source may be performed according to conventional methods in the art. For example, the sol-gel reaction may be performed 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 according to the metal oxide source, surfactant, etc. used. For example, the solvent may be an alcohol compound such as ethanol and isopropanol. In addition, a small amount of water may be added to the solvent to adjust the hydrolysis rate and thus the morphology of the metal oxide layer produced. In particular, the solvent may be ethanol, the volume ratio of ethanol to water may be 10:1-100:1.
in addition, catalysts, such as bases (e.g., ammonia), may be added to the sol-gel reaction.
In addition, the sol-gel reaction may be performed in the presence of a stabilizer (e.g., hydroxypropyl cellulose) to maintain stability of the nanoparticles.
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), siO may be used as a catalyst in the following step 2 Deposition of metal oxides (e.g., tiO) on nanosphere template surfaces 2 Or ZrO(s) 2 ) A layer forming a material A of SiO 2 Nanosphere template @ metal oxide (e.g., siO 2 @TiO 2 Or SiO 2 @ZrO 2 ) A nanocomposite.
Oxidation of metalsThe thickness of the material layer is not particularly limited, and may be prepared by selecting a suitable method and conditions according to the size required for the application field, for example, may be 5 to 50nm, for example, 10 to 50nm,20 to 40nm, etc., but is not limited thereto. For example, by controlling the amount of metal oxide source (e.g., titanium source or zirconium source) added, the metal oxide (e.g., tiO 2 Or ZrO(s) 2 ) Thickness of the layer.
Step (2)
In this step, the material A obtained in the step (2) is treated with an aqueous alkali metal hydroxide solution (e.g., naOH, KOH aqueous solution) to obtain a material B into which alkali metal ions are introduced.
Part of the metal in the metal oxide prepared in step (1) is replaced by alkali metal under the action of an aqueous alkali metal hydroxide solution (e.g. part of Ti is replaced by Na which is intercalated into TiO by replacing the Ti site 2 In) to thereby obtain a metal oxide-alkali metal (e.g., tiO) X -alkali metal) structure, providing sites for subsequent ion exchange.
In some embodiments, the molar ratio of the alkali metal hydroxide added in step (2) to the 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, the molar ratio of which is too small, may result in NaOH failing to sufficiently destroy the amorphous (not forming a crystalline structure) metal oxide (e.g., tiO 2 ) And thus cannot generate enough ion exchange sites, and if the ratio is too large, the morphology of the hollow nanospheres is seriously affected.
In some embodiments, the treatment time of material a with the aqueous alkali metal hydroxide solution may be from 1 to 6 hours.
In step (2), the metal oxide is prepared by substituting a part of the metal (e.g., tiO 2 Part of Ti or ZrO in 2 Part Zr) of (B) to form a material B which is SiO 2 Nanosphere templates @ metal oxide-alkali metal ions (e.g., siO 2 @TiO 2 -Na + Or SiO 2 @ZrO 2 -Na + ) A nanocomposite.
In some embodiments, step (2) is performed as follows:
to the aqueous dispersion of the material a, an aqueous NaOH solution was added for treatment, followed by solid-liquid separation.
The solid-liquid separation can be performed by centrifugation. The centrifugation speed is not particularly limited as long as the aqueous NaOH solution and the solid material can be separated as much as possible, and may be 8000rpm, for example, but is not limited thereto.
In addition, 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 means in the art may be employed.
Step (3)
In this step, the alkali metal ion-introduced material B is treated with an aqueous solution of a metal salt so that the metal ion of the metal salt is cation-exchanged with the alkali metal ion previously substituted into the metal oxide to obtain a metal ion-introduced material C.
The metal of the metal salt may be a metal element known in the art for use as a catalyst active component, including but not limited to transition metal elements of the fourth, fifth, sixth periods of the periodic table, such as Fe, ni, cu, co, ag, pt, pd, etc. The metal salt may be a water-soluble salt of a metal, such as nitrate, sulfate, 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 12-24 hours.
In some embodiments, step (3) is performed as follows: adding metal nitrate aqueous solution into the water dispersion of the material B to react, thus obtaining the material C.
Thereby, metal ions of the metal salt are introduced into the metal oxide (e.g., tiO 2 Or ZrO(s) 2 ) In (C) is obtained as a composite material, denoted as SiO 2 Nanosphere template @ metal oxide-M n+ (e.g. SiO) 2 @TiO 2 -M n+ Or SiO 2 @ZrO 2 -M n+ ) Wherein M is n+ Represents a metal ion, wherein n represents the valence of the metal ion, which is not particularly limited and may be 1 or 2 or 3, such as Fe 2+ 、Fe 3+ 、Ni 2+ 、Cu 2+ 、Co 2+ 、Ag + 、Pt 2+ 、Pd 2+ 。
Step (4)
In this step, the material C (i.e., siO 2 Nanosphere template @ metal oxide-M n+ ) Surface deposition of SiO 2 A layer of molding material, to obtain material D, namely SiO 2 Nanosphere template @ metal oxide-M n+ @SiO 2 Layer of molding material (e.g. SiO 2 @TiO 2 -M n+ @SiO 2 Or SiO 2 @ZrO 2 -M n+ @SiO 2 )。
By controlling the reaction conditions, e.g. SiO 2 The addition amount, the reaction temperature, the reaction time and the like of the precursor are used for controlling the SiO 2 Thickness of the layer of molding material. SiO (SiO) 2 The thickness of the layer of template material may generally be from 5 to 500nm, for example from 5 to 50nm, for example from 10 to 50nm, from 20 to 40nm, etc.
Furthermore, siO is deposited 2 The template material layer may be performed in the presence of a stabilizer, such as polyvinylpyrrolidone (PVP), to maintain stability of the nanoparticles.
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 was carried out in the presence of material C having PVP adsorbed on the surface 2 Sol-gel reaction of precursors to deposit SiO on the surface of PVP-adsorbed material C 2 Die plateAnd (5) a material layer.
SiO 2 The sol-gel reaction of the precursor may be performed according to conventional methods in the art. SiO (SiO) 2 The precursor may be SiO selected conventionally in the art 2 The 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, siO deposition on the surface of material C may be achieved by sequentially adding water, tetraethoxysilane, and ammonia to material C having PVP adsorbed on the surface in a solvent system of ethanol 2 And (5) a die material layer.
Preferably, the molar ratio of the metal oxide source added in step (1) to PVP added here may be 70:1-700:1.
step (4) may further comprise depositing SiO 2 And (3) carrying out solid-liquid separation on the material after the material layer of the die plate material, and drying the solid after obtaining the solid. The drying method is not particularly limited as long as it is suitable for preparing the catalyst. For example, vacuum drying, spray drying, and the like may be used, but the present invention is not limited thereto.
Step (5)
In this step, material D is calcined under an inert atmosphere to give material E, i.e., siO 2 Nanosphere template @ metal oxide-M 1 @SiO 2 Layer of molding material (e.g. SiO 2 @TiO 2 -M 1 @SiO 2 Or SiO 2 @ZrO 2 -M 1 @SiO 2 ) A nanocomposite. Wherein M is 1 Representing a metal monoatom.
The inert atmosphere may be a nitrogen atmosphere or an argon atmosphere. The calcination temperature is 600-900 ℃, the temperature rising rate is 1-5 ℃/min, and the calcination time is 1-3 hours. The metal ion M can be calcined under an inert atmosphere n+ Conversion to metal monoatoms M 1 。
Step (6)
In this step, siO in material E is removed 2 Nanosphere templates and SiO 2 A template material layer to obtain a metal oxide-based metal monoatomic catalyst with a mesoporous hollow nanosphere structure, namely metal oxide-M 1 (e.g. TiO) 2 -M 1 Or ZrO(s) 2 -M 1 ) Monoatomic catalysts (also sometimes denoted as M 1 Metal oxides, e.g. M 1 /TiO 2 Or M 1 /ZrO 2 )。
For example, siO 2 Nanosphere templates and SiO 2 The template material layer may be removed by full etching of the template material. The etchant may be known in the art to etch SiO 2 Including but not limited to aqueous NaOH.
In some embodiments, the etchant NaOH is combined with the SiO added in step (4) 2 The molar ratio of the precursor (e.g., tetraethoxysilane) may be 1.5 to 3. The etching temperature is not particularly limited and may be performed at 30 to 120 ℃, for example.
Without being bound by any theory, the inventors believe that in the preparation method of the present invention, under the action of alkali metal hydroxide (e.g., naOH), a metal element of a part of the metal oxide (e.g., tiO 2 Ti) of (a) is substituted with an alkali metal ion (e.g. Na + ) Substituted, forming metal oxide-alkali metal ions (e.g. TiO X -Na + ) The structure of (a) is that after the metal salt is added, the metal ion is combined with alkali metal ion (such as Na + ) Ion exchange takes place and cooperates with the outer SiO layer 2 The space limiting function of the template material layer is used for avoiding the agglomeration of metal atoms in the calcination process, so that the metal oxide base (such as ZrO 2 And TiO 2 Radical) metal monoatomic catalysts. Thus, in the present invention, the outer SiO layer is coordinated by an alkali metal hydroxide (e.g., naOH) -assisted ion exchange process 2 Space-limiting action of the template material, i.e. fixing metal atoms to Ti or Zr sites by ion exchange on the one hand and SiO coated by the outer layer on the other hand 2 The metal atoms are limited in a limited space, and the metal atoms cooperate to ensure that the metal atoms are not easy to calcine at high temperatureAnd (5) moving the agglomeration.
The metal oxide-based metal monoatomic catalyst of the invention mainly comprises metal monoatom M 1 And metal oxides, but may also be present in part other substances, e.g. non-removed SiO 2 Or a portion of the metal ions.
In some embodiments, the metal oxide is TiO 2 Or ZrO(s) 2 The metal is selected from transition metal elements of the fourth, fifth and sixth periods of the periodic table, such as Fe, ni, cu, co, etc., and the method for preparing a metal oxide-based metal monoatomic catalyst of the present invention comprises the steps of:
(1) In SiO 2 Deposition of TiO on nanosphere surfaces 2 Or ZrO(s) 2 Layer (c): in SiO 2 Adding a titanium source or a zirconium source into an ethanol water solution in the presence of nanospheres and hydroxypropyl cellulose to carry out sol-gel reaction to obtain SiO 2 @TiO 2 Or SiO 2 @ZrO 2 ；
(2) Treatment of SiO with aqueous NaOH solution 2 @TiO 2 Or SiO 2 @ZrO 2 SiO is obtained 2 @TiO 2 -Na + Or SiO 2 @ZrO 2 -Na + The method comprises the steps of carrying out a first treatment on the surface of the Wherein, the mol ratio of NaOH to the titanium source or the zirconium source is 1:1-16:1, a step of;
(3) Treatment of SiO with aqueous Metal salt solutions 2 @TiO 2 -Na + Or SiO 2 @ZrO 2 -Na + SiO is obtained 2 @TiO 2 -M n+ Or SiO 2 @ZrO 2 -M n+ The method comprises the steps of carrying out a first treatment on the surface of the Wherein, the mol ratio of NaOH to metal salt is 0.8:1-20:1, a step of;
(4) SiO is made of 2 @TiO 2 -M n+ Or SiO 2 @ZrO 2 -M n+ Adsorbing PVP on the surface, and adsorbing SiO with PVP on the surface 2 @TiO 2 -M n+ Or SiO 2 @ZrO 2 -M n+ SiO in the presence of 2 Sol-gel reaction of the precursor to obtain SiO 2 @TiO 2 -M n+ @SiO 2 Or SiO 2 @ZrO 2 -M n+ @SiO 2 ；
(5) SiO is made of 2 @TiO 2 -M n+ @SiO 2 Or SiO 2 @ZrO 2 -M n+ @SiO 2 Calcining under inert atmosphere to obtain SiO 2 @TiO 2 -M 1 @SiO 2 Or SiO 2 @ZrO 2 -M 1 @SiO 2 ；
(6) Removal of SiO with aqueous NaOH solution 2 @TiO 2 -M 1 @SiO 2 Or SiO 2 @ZrO 2 -M 1 @SiO 2 SiO of (C) 2 Obtaining TiO 2 -M 1 Or ZrO(s) 2 -M 1 Monoatomic catalysts (sometimes also referred to as M) 1 /TiO 2 Or M 1 /ZrO 2 )。
The invention also provides the metal oxide-based metal monoatomic catalyst prepared by the method. In some embodiments, the description of the metal oxide-based metal monoatomic catalyst is the same as that described above, and will not be repeated here.
The catalyst of the invention can be applied to different fields such as thermocatalytic hydrogenation, thermocatalytic oxidation, electrocatalysis, photocatalysis, nano-enzyme-like catalysis, photoelectrocatalysis and the like according to the catalytic activity of metal.
In a further aspect, the invention provides the use of a metal oxide-based metal monoatomic catalyst according to the invention or a metal oxide-based metal monoatomic catalyst prepared according to the process of the invention in catalytic hydrogenation, in particular in the preparation of phenylpropionaldehyde by catalytic hydrogenation of cinnamaldehyde.
The metal oxide-based metal monoatomic catalyst can be used in any catalytic hydrogenation and has wide application prospect. Taking catalytic hydrogenation of cinnamaldehyde to prepare phenylpropionaldehyde as an example, the method has the advantages of higher conversion rate of cinnamaldehyde hydrogenation and selectivity of phenylpropionaldehyde, and high cycle stability.
In a preferred embodiment, the method for selectively hydrogenating cinnamaldehyde according to the present invention comprises the steps of: the cinnamaldehyde is subjected to a hydrogenation reaction in the presence of the metal oxide-based monoatomic catalyst according to the invention or the metal oxide-based monoatomic catalyst prepared according to the process of the invention. The method has high conversion rate of cinnamaldehyde hydrogenation and selectivity of phenylpropionaldehyde, and high cycle stability.
In the above-described method, the temperature, time and pressure of the reaction may be the conventional reaction conditions for the hydrogenation reaction without particular limitation. For example, the reaction temperature may be 90-140 ℃ (e.g., 100, 120, 130 ℃), the time may be 1-3 hours, and the pressure may be 0.4-4MPa.
Advantageous effects
(1) The catalyst metal is loaded on the metal oxide in a single atom 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 in catalytic hydrogenation of cinnamaldehyde to prepare phenylpropionaldehyde, and has higher conversion rate of cinnamaldehyde hydrogenation and selectivity of phenylpropionaldehyde, and high cycle stability.
(2) The invention prepares SiO as catalyst 2 Is used as a template and utilizes an NaOH-assisted ion exchange process with an inert outer layer (SiO 2 Template layer) of the metal atoms (on the one hand, the metal atoms are fixed at Ti or Zr sites by an ion exchange process, on the other hand, siO coated with an outer layer 2 The metal atoms are limited in a limited space and cooperate with each other, so that the metal is not easy to agglomerate in the calcining process, and the acid treatment process is not needed, thus synthesizing the metal oxide (ZrO) with the mesoporous hollow nanosphere structure 2 And TiO 2 ) The single-atom-based catalyst has the advantages of low cost, high activity, high selectivity and good cycle stability.
(3) The monoatomic preparation method can effectively inhibit the generation of metal nano particles, avoids the resource waste in the acid treatment process, provides a new thought for the synthesis of the monoatomic catalyst, and simultaneously provides more possibilities for the industrial application of the monoatomic catalyst.
(4) The method provided by the invention has wider universality, can be suitable for various metal monoatoms, and ensures that the metal loading capacity under the monoatoms 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 exemplary 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 summary or the following examples.
Unless explicitly stated otherwise, numerical ranges throughout this application include any subrange therein and any numerical value incremented by the smallest subunit in which a given value is present. Unless explicitly stated otherwise, numerical values throughout this application represent approximate measures or limits to include minor deviations from the given value and ranges of embodiments having about the stated value and having the exact value noted. Except in the operating examples provided last, all numerical values of parameters (e.g., amounts or conditions) in this application (including the appended claims) are to be understood in all cases as modified by the term "about" whether or not "about" actually appears before the numerical value. "about" means that the recited value allows for slight imprecision (with some approximation to the exact value; approximately or reasonably close to the value; approximated). "about" as used herein at least means variations that can be produced by ordinary methods of measuring and using these parameters if the imprecision provided by "about" is not otherwise understood in the art with this ordinary meaning. For example, "about" may include a change 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 obtained in example 1 of the present invention 1 /TiO 2 Is a lens image of the lens.
FIG. 2 shows Ni obtained in example 2 of the present invention 1 /ZrO 2 Is a lens image of the lens.
FIG. 3 shows Ni obtained in example 1 of the present invention 1 /TiO 2 Is an X-ray diffraction pattern of (2).
FIG. 4 shows Ni obtained in example 2 of the present invention 1 /ZrO 2 Is an X-ray diffraction pattern of (2).
FIG. 5 showsNi prepared in example 1 of the present invention 1 /TiO 2 Spherical aberration correcting high angle annular dark field scanning transmission electron microscope (HAADF-STEM) photographs of single atom catalysts.
FIG. 6 shows Ni prepared in example 2 of the present invention 1 /ZrO 2 Spherical aberration correcting high angle annular dark field scanning transmission electron microscope (HAADF-STEM) photographs of single atom catalysts.
Detailed Description
The 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 as claimed.
Unless otherwise indicated, all materials, reagents, methods and the like used in the examples are those conventionally used in the art.
Tetraethoxysilane: alfa Aesar;
n-butyl titanate, n-butyl zirconate: j & K;
inductively coupled plasma spectrometer: model iCAP 6000series;
transmission electron microscope: model JEOL JEM-1200, acceleration voltage is 100KV;
x-ray diffractometer: model Bruker AXS D8-Advanced;
spherical aberration correcting transmission electron microscope: model Titan Cubed Themis G2 300.
Example 1: ni (Ni) 1 /TiO 2 Synthesis
SiO 2 Is synthesized by the following steps: 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 poured 2 O, stirring for 3 min, and injecting 0.8mL NH 3 ·H 2 O. After 4 hours of reaction, the reaction mixture was centrifuged 3 times (8000 rpm,5 minutes) with ethanol, and finally the product was dispersed in 10mL of ethanol.
SiO 2 @TiO 2 Is synthesized by the following steps: 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 last step 2 Injection into reactionAfter 10 minutes, 0.2mL NH was injected into the solution 3 ·H 2 O, over 10 minutes, was injected with TBOT buffer (1 mL TBOT,3mL high purity ethanol (. Gtoreq.99.5%), 1mL high purity acetonitrile (. Gtoreq.99.9%), and after 2 hours of reaction, the product was collected by centrifugation (3 times with ethanol followed by three times with water, 8000rpm,5 minutes).
SiO 2 @TiO 2 -Ni 2+ : treatment with 10. Mu.L of 2.5mol/L NaOH was carried out for 30 minutes, and after reaction was carried out for 2 times with deionized water, the reaction was dispersed in 40mL of deionized water, then 500. Mu.L of 0.05mol/L aqueous solution of nickel nitrate hexahydrate was added, and the reaction was carried out for 12 hours, and then the reaction was carried out for 3 times with deionized water (8000 rpm,5 minutes).
SiO 2 @TiO 2 -Ni 2+ @SiO 2 Is synthesized by the following steps: 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 H 2 O), stirring for 12 hours to make PVP fully adsorbed on TiO 2 Is a surface of the substrate. Centrifugal collection with deionized water (will not adsorb onto TiO) 2 The PVP on the surface is removed. 800 rpm,5 minutes); dispersing the PVP-adsorbed sample in 23mL ethanol, adding 4.3mL deionized water, stirring for 3 min, adding 0.86mL TEOS, stirring for 3 min, and adding 0.8mL NH 3 ·H 2 After 3 hours of reaction, O was centrifuged three times with ethanol, and the product was collected (8000 rpm,5 minutes) and then dried in a vacuum oven for the next step.
High-temperature calcination: grinding the dried sample into powder, placing into a porcelain boat, transferring the porcelain boat into a tube furnace, and introducing N 2 Removing air in the tube furnace, heating after 30 minutes, setting the heating rate to be 5 ℃/min, keeping for 2 hours at 800 ℃, and taking out the porcelain boat after the porcelain boat is naturally cooled to room temperature.
Ni 1 /TiO 2 Dispersing the calcined sample in deionized water, adding enough 2.5mol/L NaOH aqueous solution, heating to 90 ℃ in an oil bath, introducing condensed water for reflux, and reacting until SiO is completely removed 2 The template is centrifuged by deionized water to remove redundant Na + Until the pH of the supernatant is neutral, drying in a vacuum oven at 60deg.C for 12 hr, taking out, and grinding into powder in a mortar to obtain Ni 1 /TiO 2 Monoatomic catalysts.
Ni measurement by inductively coupled plasma emission spectrometer 1 At Ni 1 /TiO 2 The loading on the catalyst was 0.4wt%.
Example 2: ni (Ni) 1 /ZrO 2 Is synthesized by (a)
SiO 2 Is synthesized by the following steps: as in example 1.
SiO 2 @ZrO 2 Is synthesized by the following steps: first, 20mL of ethanol and 0.1mL of H were added to a 50mL Erlenmeyer flask 2 O, stirring for 3 min, adding 10mg of hydroxypropyl cellulose, stirring for 10 min, and after the hydroxypropyl cellulose is completely dissolved, adding the SiO synthesized in the last step 2 After 20 minutes of injection into the reaction solution, ZBOT buffer (0.6 mL of ZBOT,4.4mL of ethanol) was injected, and after 20 hours of reaction, the product was collected by centrifugation (2 times with ethanol followed by 2 times with water, 8000rpm,4 minutes).
SiO 2 @ZrO 2 -Ni 2+ Is synthesized by the following steps: treatment with 10. Mu.L of 2.5mol/L NaOH was carried out for 30 minutes, and after reaction was carried out for 2 times with deionized water, the reaction was dispersed in 40mL of deionized water, then 500. Mu.L of 0.05mol/L aqueous solution of nickel nitrate hexahydrate was added, and the reaction was carried out for 12 hours, and then the reaction was carried out for 3 times with deionized water (8000 rpm,5 minutes).
SiO 2 @ZrO 2 -Ni 2+ @SiO 2 Is synthesized by the following steps: as in example 1.
High-temperature calcination: as in example 1.
Ni 1 /ZrO 2 Is synthesized by the following steps: ni was measured by inductively coupled plasma emission spectrometer as in example 1 1 At Ni 1 /ZrO 2 The loading on the catalyst was 0.5wt%.
Characterization by transmission electron microscope:
FIGS. 1 and 2 show Ni obtained in example 1 1 /TiO 2 And Ni prepared in example 2 1 /ZrO 2 Can observe Ni by Transmission Electron Microscope (TEM) photograph 1 /TiO 2 And Ni 1 /ZrO 2 The appearance of the polymer is hollow nanospheres. For the Ni prepared 1 /TiO 2 And Ni 1 /ZrO 2 Multiple angle observations were made on electron microscope samples of (C) and were not made on TiO 2 And ZrO(s) 2 Ni or other nanoparticles were observed on the support surface.
Characterization by using a spherical aberration electron microscope:
ni prepared in examples 1 and 2, respectively 1 /TiO 2 And Ni 1 /ZrO 2 Characterization was performed with a spherical aberration microscope as shown in fig. 5 and 6. Ni exists in the form of independent obvious bright spots in the spherical aberration electron microscope, and the fact that the metal Ni is dispersed in the form of monoatoms in TiO is proved 2 And ZrO(s) 2 In a carrier.
The single atom is present in a manner coordinated to O on the metal oxide support.
Characterization by X-ray diffraction:
examples 1 and 2 respectively produce Ni 1 /TiO 2 And Ni 1 /ZrO 2 The X-ray diffraction patterns of (a) are shown in fig. 3 and 4. Illustrating TiO 2 The crystalline phase of (2) is anatase phase, zrO 2 The crystalline phase of (a) is a tetragonal phase.
Example 3: fe (Fe) 1 /TiO 2 Is synthesized by (a)
Other conditions and steps of this example are the same as those of example 1 except that the aqueous nickel nitrate hexahydrate solution is replaced with an equal concentration and equal volume aqueous nickel nitrate hexahydrate solution.
Example 4: fe (Fe) 1 /ZrO 2 Is synthesized by (a)
Other conditions and steps of this example are the same as those of example 2 except that the aqueous nickel nitrate hexahydrate solution is replaced with an equal concentration and equal volume of aqueous nickel nitrate hexahydrate solution.
Example 5: cu (Cu) 1 /TiO 2 Is synthesized by (a)
Other conditions and steps of this example are the same as those of example 1 except that the aqueous solution of nickel nitrate hexahydrate is replaced with an equal concentration and equal volume of aqueous solution of copper nitrate hexahydrate.
Example 6: cu (Cu) 1 /ZrO 2 Is synthesized by (a)
Other conditions and steps of this example are the same as those of example 2 except that the aqueous solution of nickel nitrate hexahydrate is replaced with an equal concentration and equal volume of aqueous solution of copper nitrate hexahydrate.
Example 7: co (Co) 1 /TiO 2 Is synthesized by (a)
Other conditions and steps of this example were the same as in example 1 except that the aqueous solution of nickel nitrate hexahydrate was replaced with an equal concentration and equal volume of aqueous solution of cobalt nitrate hexahydrate.
Example 8: co (Co) 1 /ZrO 2 Is synthesized by (a)
Other conditions and steps of this example were the same as in example 2 except that the aqueous solution of nickel nitrate hexahydrate was replaced with an equal concentration and equal volume of aqueous solution of cobalt nitrate hexahydrate.
Example 9: ag (silver) 1 /TiO 2 Is synthesized by (a)
Other conditions and steps of this example were the same as in example 1 except that the aqueous solution of nickel nitrate hexahydrate was replaced with an equal concentration and equal volume of aqueous solution of silver nitrate hexahydrate.
Example 10: ag (silver) 1 /ZrO 2 Is synthesized by (a)
Other conditions and steps of this example were the same as in example 2 except that the aqueous solution of nickel nitrate hexahydrate was replaced with an equal concentration and equal volume of aqueous solution of silver nitrate hexahydrate.
Example 11: pt (Pt) 1 /TiO 2 Is synthesized by (a)
Other conditions and steps 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 and equal volume of platinum tetrammine nitrate aqueous solution.
Example 12: pt (Pt) 1 /ZrO 2 Is synthesized by (a)
Other conditions and steps 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 and equal volume of platinum tetrammine nitrate aqueous solution.
Example 13: pd (Pd) 1 /TiO 2 Is synthesized by (a)
Other conditions and steps of this example are the same as those of example 1, except that the nickel nitrate hexahydrate aqueous solution is replaced with an equal concentration and equal volume of palladium nitrate aqueous solution.
Example 14: pd (Pd) 1 /ZrO 2 Is synthesized by (a)
Other conditions and steps of this example are the same as those of example 2, except that the nickel nitrate hexahydrate aqueous solution is replaced with an equal concentration and equal volume of palladium nitrate aqueous solution.
Comparative example 1: ni (Ni) nps /TiO 2 Is synthesized by (a)
Other conditions and steps of this comparative example were the same as in example 1, except that the volume of the aqueous solution of nickel nitrate hexahydrate was increased ten times.
Comparative example 2: ni (Ni) nps /ZrO 2 Is synthesized by (a)
Other conditions and steps of this comparative example were the same as in example 2, except that the volume of the aqueous solution of nickel nitrate hexahydrate was increased ten times.
Comparative example 3: ni (Ni) nps /SiO 2 Is synthesized by (a)
Using commercial SiO 2 Is synthesized by a simple impregnation method.
Application example
The catalysts prepared in examples and comparative examples were used for cinnamaldehyde hydrogenation. The specific process is as follows:
sequentially adding 25.0mg of catalyst, 50 mu L of reactant cinnamaldehyde and 25.0mL of isopropanol into a 100mL reaction kettle liner, installing the reaction kettle, and filling and discharging H after ensuring that the reaction kettle is completely sealed 2 5 times (about 1MPa of H is introduced each time) 2 ) Exhausting the air in the reaction kettle and then introducing 3MPa H 2 The 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, taking out the liner, adding about 50mg of internal standard biphenyl, taking out about 2.0mL of the reacted solution by using a syringe after the biphenyl is completely dissolved, filtering out impurities such as catalyst powder by using a filter membrane, diluting by a certain multiple (ensuring that the concentration of the reactant is lower than 100 ppm), injecting the diluted solution by using a microsyringe, and analyzing the content of a product by using gas chromatography.
The conversion was calculated as follows:
conversion% = cinnamaldehyde consumption before and after reaction/cinnamaldehyde feed x 100%;
the selectivity is calculated as follows:
selectivity% = molar amount of phenylpropionaldehyde/total molar amount of cinnamyl alcohol, phenylpropionaldehyde and phenylpropanol x 100%.
As shown in tables 1, 2 and 3, wherein COL represents cinnamyl alcohol, HCAL represents phenylpropionaldehyde, and HCOL represents phenylpropanol.
TABLE 1
Figure BDA0003519151160000121
TABLE 2
Figure BDA0003519151160000122
TABLE 3 Table 3
Figure BDA0003519151160000123
The results show that Ni in the prepared catalyst 1 /TiO 2 Shows the most excellent catalytic performance at 130 ℃ and 3MPa H 2 Under the reaction condition of 2 hours, the conversion rate of cinnamaldehyde can reach 98 percent and the selectivity of phenylpropionaldehyde can reach 90 percent.
The above embodiments are only for illustrating the technical solution of the present invention, and are not limited thereto. Although the invention has been described in detail with reference to the foregoing embodiments, it will be understood by those of ordinary skill in the art that: modifications may be made to the technical solutions described in the foregoing embodiments, or equivalents may be substituted for some or all of the technical features thereof, without departing from the spirit and scope of the present invention as defined in the claims; and such modifications or substitutions are intended to be within the scope of the present invention as defined by the claims.

Claims (14)

1. A method for preparing a metal oxide-based metal monoatomic catalyst for catalytic hydrogenation is characterized in that,
the metal oxide-based metal monoatomic catalyst includes: a metal oxide, which is a morphology of mesoporous hollow nanospheres, and a metal, which is supported on the metal oxide in a form of a single atom;
the preparation method of the metal oxide-based metal monoatomic catalyst comprises the following steps:
(1) In SiO 2 In the presence of nanospheres, a metal oxide source is used as a precursor to carry out sol-gel reaction, thereby obtaining SiO (silicon dioxide) 2 Depositing a metal oxide layer on the nanospheres to form a material A; wherein the metal oxide source is a titanium source or a zirconium source;
(2) Treating the material A in the step (1) with an alkali metal hydroxide aqueous solution to obtain a material B into which alkali metal ions are introduced;
(3) Treating the material B in the step (2) with an aqueous solution of a metal salt to obtain a material C into which metal ions are introduced; the metal in the metal salt is Ni;
(4) Mixing the material C in the step (3) with polyvinylpyrrolidone in water to obtain a material C with polyvinylpyrrolidone adsorbed on the surface; siO is carried out in the presence of a material C having polyvinylpyrrolidone adsorbed on the surface 2 Sol-gel reaction of the precursor to deposit SiO on the surface of the polyvinylpyrrolidone-adsorbed material C 2 A die plate material layer to obtain a material D;
(5) Calcining the material D in an inert atmosphere to obtain a material E; wherein the calcination temperature is 600-900 ℃;
(6) Removing SiO in material E by NaOH aqueous solution etching 2 Nanospheres and SiO 2 A template material layer to obtain a metal oxide-based metal monoatomic catalyst with a mesoporous hollow nanosphere structure;
the loading of Ni monoatoms is within 0.5wt% based on the total weight of the metal oxide based metal monoatom catalyst.
2. The method of claim 1, wherein the step of determining the position of the substrate comprises,
SiO in step (1) 2 The diameter of the nanospheres is 40-900 nm; and/or
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; and/or
The thickness of the metal oxide layer is 5-50 a nm a.
3. The method of claim 1, wherein the step of determining the position of the substrate comprises,
SiO in step (1) 2 The diameter of the nanospheres is 60-500 nm; and/or
The thickness of the metal oxide layer is 10-50 a nm a.
4. The method of claim 1, wherein the step of determining the position of the substrate comprises,
SiO in step (1) 2 The diameter of the nanospheres is 100-400 nm; and/or
The thickness of the metal oxide layer is 20-40 a nm a.
5. The method of claim 1, wherein the step of determining the position of the substrate comprises,
in the step (2), the alkali metal hydroxide is one or more selected from NaOH and KOH; and/or
In the step (3), the metal salt is one or more selected from nitrate, sulfate and hydrochloride.
6. The method of claim 5, wherein the step of determining the position of the probe is performed,
in the step (2), the alkali metal hydroxide is NaOH.
7. The method of claim 1, wherein the step of determining the position of the substrate comprises,
the molar ratio of the alkali metal hydroxide added in step (2) to the metal oxide source added in step (1) is 1:1-16:1, a step of; and/or
The molar ratio of the alkali metal hydroxide added in step (2) to the metal salt added in step (3) is 0.8:1-20:1.
8. the method of claim 1, wherein the step of determining the position of the substrate comprises,
in the step (5), the inert atmosphere is nitrogen atmosphere or argon atmosphere; and/or
In the step (5), the temperature rising rate of calcination is 1-5 ℃/min; and/or
In the step (5), the calcination time is 1-3 hours; and/or
In the step (6), the etching temperature is 30-120 ℃.
9. The method according to claim 1, comprising the steps of:
(1) In SiO 2 Deposition of TiO on nanosphere surfaces 2 Or ZrO(s) 2 Layer (c): in SiO 2 Adding a titanium source or a zirconium source into an ethanol water solution in the presence of nanospheres and hydroxypropyl cellulose to carry out sol-gel reaction to obtain SiO 2 @TiO 2 Or SiO 2 @ZrO 2 ；
(2) Treatment of SiO with aqueous NaOH solution 2 @TiO 2 Or SiO 2 @ZrO 2 SiO is obtained 2 @TiO 2 -Na + Or SiO 2 @ZrO 2 -Na + The method comprises the steps of carrying out a first treatment on the surface of the Wherein, the mol ratio of NaOH to the titanium source or the zirconium source is 1:1-16:1, a step of;
(3) Treatment of SiO with aqueous Metal salt solutions 2 @TiO 2 -Na + Or SiO 2 @ZrO 2 -Na + SiO is obtained 2 @TiO 2 -M n+ Or SiO 2 @ZrO 2 -M n+ The method comprises the steps of carrying out a first treatment on the surface of the Wherein, the mol ratio of NaOH to metal salt is 0.8:1-20:1, a step of;
(4) SiO is made of 2 @TiO 2 -M n+ Or SiO 2 @ZrO 2 -M n+ Adsorbing polyvinylpyrrolidone on the surface, and adsorbing SiO with polyvinylpyrrolidone on the surface 2 @TiO 2 -M n+ Or SiO 2 @ZrO 2 -M n+ SiO in the presence of 2 Precursor bodySol-gel reaction to give SiO 2 @TiO 2 -M n+ @SiO 2 Or SiO 2 @ZrO 2 -M n+ @SiO 2 ；
(5) SiO is made of 2 @TiO 2 -M n+ @SiO 2 Or SiO 2 @ZrO 2 -M n+ @SiO 2 Calcining under inert atmosphere to obtain SiO 2 @TiO 2 -M 1 @SiO 2 Or SiO 2 @ZrO 2 -M 1 @SiO 2 ；
(6) Removal of SiO with aqueous NaOH solution 2 @TiO 2 -M 1 @SiO 2 Or SiO 2 @ZrO 2 -M 1 @SiO 2 SiO of (C) 2 Obtaining TiO 2 -M 1 Or ZrO(s) 2 -M 1 Monoatomic catalysts.
10. The method of claim 1, wherein the step of determining the position of the substrate comprises,
the loading of Ni monoatoms is 0.05 to 0.45wt% based on the total weight of the metal oxide based metal monoatomic catalyst.
11. The method of claim 10, wherein the step of determining the position of the first electrode is performed,
the loading of Ni monoatoms is 0.1 to 0.4wt% based on the total weight of the metal oxide based metal monoatomic catalyst.
12. Use of a metal oxide-based metal monoatomic catalyst prepared according to the process of any one of claims 1 to 11 in catalytic hydrogenation.
13. The use according to claim 12, characterized in that it is the catalytic hydrogenation of cinnamaldehyde to phenylpropionaldehyde.
14. The use according to claim 13, characterized by the steps of: subjecting cinnamaldehyde to a hydrogenation reaction in the presence of the metal oxide-based monoatomic catalyst prepared according to the method of any one of claims 1 to 11.
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CN114054063B (en) * 2021-10-26 2023-11-21 北京化工大学 Method for synthesizing monoatomic catalytic material with asymmetric double-ligand structure by nanocrystalline in-situ cladding-pyrolysis

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