CN116371411A - A copper-based catalyst supporting Cu atomic clusters or Cu single atoms with a mixed carrier and its application - Google Patents

Abstract

The invention discloses a copper-based catalyst loaded with Cu atom clusters or Cu single atoms by a mixed carrier, which comprises a carrier and an active component, wherein the carrier is silicon dioxide and substances with surface oxygen defects, and the mass ratio of the silicon oxide to the substances with surface oxygen defects is 1 (3.6-7.2); the active component is a copper species, the copper species is Cu atom clusters composed of Cu monoatoms and/or Cu atoms, the Cu atom clusters are smaller than 0.8nm in size, and the loading amount of the copper species is 5% -7% based on the total mass of the copper-based catalyst. The copper-based catalyst of the invention is used in oxalic acid IIThe methyl ester hydrogenation reaction has good effect on the selective hydrogenation production of intermediate methyl glycolate. Wherein Cu consisting of three copper atoms ₃ The cluster is a catalyst, and when the reaction temperature is 200 ℃, the reaction pressure is 2.5MPa, and the molar ratio of the fed hydrogen to the ester is 80, the yield of the intermediate product methyl glycolate reaches 95 percent, which is far higher than that of the copper-based catalyst reported in the prior art, and the catalytic activity of the intermediate product methyl glycolate is equivalent to that of the noble metal silver-based catalyst.

Description

A copper-based catalyst supporting Cu atomic clusters or Cu single atoms with a mixed carrier and its use

technical field

The invention belongs to the technical field of copper-based catalysts, and in particular relates to a copper-based catalyst that supports Cu atomic clusters or Cu single atoms on a mixed carrier and its application.

Background technique

As an important chemical raw material or solvent, methyl glycolate is widely used in the production of chemicals, medicines, pesticides, spices and dyes, and its market prospect is broad. At present, the main process for producing methyl glycolate is the catalytic coupling reaction of methyl formate and formaldehyde or polyoxymethylene to generate methyl glycolate. However, since this catalytic reaction requires the use of a liquid strong acid catalyst, this process has the problems of severe equipment corrosion, heavy pollution, and limited source of raw materials. The process of using synthesis gas to couple carbon monoxide to produce dimethyl oxalate and further hydrogenation to produce methyl glycolate has the characteristics of high atom economy, mild reaction conditions, high product selectivity, and environmental protection. One of the important routes for synthesizing methyl glycolate. Among them, the hydrogenation of dimethyl oxalate is the core of the process.

The silver-based catalyst has achieved better activity and selectivity in the process system of hydrogenation of oxalate to methyl glycolate, and its yield can often reach more than 90%. However, in silver-based catalysts, the mass fraction of metallic silver is often greater than 10%, which greatly increases the preparation cost of the catalyst, and the high-temperature hydrogen-rich conditions of the reaction easily lead to the agglomeration and deactivation of metallic silver. And when copper-based catalyst is used to hydrogenate oxalate, it is easy to make the methyl glycolate generated in the reaction be excessively hydrogenated to generate ethylene glycol, so that the yield of methyl glycolate is often lower than 84%. Therefore, in order to reduce the cost of catalyst production and obtain higher yields of methyl glycolate, it is important to design a new type of highly active copper-based catalyst to hydrogenate oxalate to generate methyl glycolate with high selectivity and yield. The key to the gas-to-methyl glycolate process technology.

The present invention aims to solve the above-mentioned problems.

Contents of the invention

The first aspect of the present invention provides a copper-based catalyst with a mixed carrier supporting Cu atomic clusters or Cu single atoms, which includes a carrier and an active component, the carrier is silica and a substance containing oxygen defects on the surface, and silica and The mass ratio of substances containing oxygen defects on the surface is 1:(3.6～7.2); the active component is a copper species, and the copper species is a Cu single atom and/or a Cu atom cluster composed of several Cu atoms, the The size of the Cu atomic cluster is less than 0.8nm, and the loading amount of the copper species is 5%-7% based on the total mass of the copper-based catalyst.

Preferably, the substance containing oxygen defects on the surface is a metal oxide containing oxygen defects on the surface, and the metal oxide containing oxygen defects on the surface is selected from cerium oxide, zinc oxide, zirconium oxide, titanium oxide or manganese oxide.

Preferably, the silicon dioxide has a layered structure, and the particle size of the substance containing oxygen defects on the surface is 4.0 nm to 20.0 nm.

Preferably, the average valence state of copper in the copper species is 0-1.

Preferably, the number of Cu atoms in the Cu atomic cluster is less than 100, preferably less than 60, more preferably less than 30, still more preferably less than 15, even more preferably less than 6, most preferably less than 3.

Wherein, the preparation method of the copper-based catalyst supporting Cu atomic clusters or Cu single atoms with a mixed carrier comprises the following steps:

(1) The material providing silica-loaded copper oxide nanoparticles is the first raw material, and the mass percentage of copper in the material of the silica-loaded copper oxide nanoparticles is 5% to 50%; the copper oxide nanoparticles Particle size is less than 4nm;

(2) The substance that provides surface oxygen-containing defects is the second raw material;

(3) mixing the second raw material with the first raw material, and performing the treatment of the first stage and the second stage after mixing; or,

The first raw material is subjected to the reduction treatment of the first stage, and then mixed with the second raw material, and then the second stage of treatment is carried out after mixing;

The reduction treatment in the first stage reduces the copper oxide nanoparticles loaded on the silica to copper nanoparticles, and the second stage treatment makes the copper nanoparticles migrate to the surface oxygen-deficient substances to form Cu single atoms or Cu atom clusters. , to obtain the copper-based catalyst.

Preferably, in step (1), the preparation method of the material of silica-loaded copper oxide nanoparticles comprises the following steps:

(11) Dissolve copper nitrate trihydrate in water, then add ammonia water, stir and mix to obtain the first mixed solution;

(12) adding silica sol dropwise to the first mixed solution, stirring, and then distilling off the ammonia component in the first mixed solution to obtain a second mixed solution;

(13) Filter the second mixed solution obtained in step (12), collect the filter cake, wash it, and roast it in an air atmosphere to obtain a silica-supported copper oxide nanoparticle substance.

Preferably, the concentration of ammonia water in step (11) is 20% to 28%; the volume ratio of ammonia water to water is 1:1.12 to 1:2.31; the temperature of distillation in step (12) is 60°C to 90°C, and the The pH of the solution after the ammonia component in the first mixed solution is 6.5-8.5.

Wherein, the addition amount of copper nitrate trihydrate and silica sol in the step (11) is designed according to the mass fraction of copper in the material of the silica-loaded copper oxide nanoparticles finally obtained, and the copper in the material of the silica-loaded copper oxide nanoparticles is The mass fraction is 5% to 50%.

The specific surface area of the first raw material prepared by the above method is 400-600m ² /g, the average pore volume is 0.3-1.1cm ³ /g, the average pore diameter is 3.0-10.0nm, and the particle size of the copper oxide nanoparticles is smaller than 4nm.

Preferably, the mass ratio of the first raw material to the second raw material in step (3) is 1:3.6 to 1:7.2;

The reduction treatment condition of the first stage is: at 180-400° C., in the first gas atmosphere, for 4-6 hours, the copper oxide nanoparticles supported on the silicon dioxide are reduced to copper nanoparticles;

The treatment conditions of the second stage are: at 180°C to 300°C, in a second gas atmosphere, for 20 to 150 hours, the copper nanoparticles migrate to the surface oxygen defect-containing substances to form Cu atomic clusters, and the copper nanoparticles are obtained. base catalyst.

Preferably, the first gas is a reducing gas, such as hydrogen; the second gas is a non-oxidizing gas, such as selected from nitrogen, hydrogen or argon; the flow rate of the first gas is 20-150mL/g material, The flow rate of the second gas flow is 10-200mL/g material.

Wherein, the migration includes the migration of various mechanisms, such as copper atom volatilization-deposition mechanism, or contact-transfer mechanism, etc., these migrated copper atoms are trapped at the oxygen defects on the surface of the material with oxygen defects And gradually grow from single atoms to copper nanoclusters. With the continuous migration of copper atoms on the copper nanoparticles, the size of the original copper nanoparticles supported on the surface of the silica is gradually reduced to the form of copper nanoclusters or even copper single atoms. In the copper-based catalyst, the above-mentioned copper single atoms and/or copper atom clusters are supported on the upper surfaces of both the silica carrier and the substance containing oxygen defects on the surface.

In the prior art prior to the present invention, the metal precursor and the reducible metal oxide carrier were mixed at high temperature and treated at high temperature, and the metal species migrated to the surface of cerium oxide to form a single Atomic species, is a common method for preparing single-atom catalysts. However, there are problems in the process of preparing copper-based catalysts using existing technologies: the copper oxide particles before migration are larger than 4nm, and copper atoms cannot migrate at low temperatures. Therefore, in order to promote the migration of copper species on silica, the migration process usually The medium treatment temperature is 600-1000°C, and the high-temperature treatment environment will cause the copper atoms migrating to the surface oxygen-deficient substances to exceed a certain amount, and will quickly agglomerate from Cu single atoms into several nanometers or even tens of nanometers, hundreds of nanometers Nano-sized copper nanoparticles, so the surface copper species cannot be obtained as Cu atomic clusters with a size smaller than 0.8nm composed of several Cu atoms.

Here, what was ignored by all prior art and noticed by the inventor is that the difference between "copper nanoparticles" and "copper clusters", although there is no strict definition recognized by the academic circles, in the present invention, the size is larger than Copper atom aggregates with a size of 2nm are called "copper nanoparticles", while copper atom aggregates with a size of less than 0.8nm are called "copper atom clusters", and copper atom aggregates with a size between 0.8 and 2nm are called "copper atom aggregates". Copper subnanoparticles". In the copper-based catalysts that have been reported by the predecessors, the active component copper exists in the form of "copper nanoparticles" or "copper sub-nanoparticles" without exception, and there is no report of the existence of "copper clusters". On the research report on the catalytic performance of the latter.

The present invention firstly prepares silica-loaded copper oxide nanoparticles as the first raw material by the ammonia distillation method, wherein the particle size of the copper oxide nanoparticles in the first raw material is less than 4nm, because the silica-loaded copper oxide The particle size of the nanoparticles is small, so that the copper oxide nanoparticles on the first raw material can be reduced to copper nanoparticles at 200-400°C and further migrate to the second raw material to form Cu single atoms and/or several Cu atoms Composed of Cu atomic clusters, the lower migration temperature prevents Cu single atoms or Cu atomic clusters from further agglomerating into copper nanoparticles, thereby obtaining the copper-based catalyst of the present invention that uses a mixed carrier to support Cu atomic clusters or Cu single atoms.

The second aspect of the present invention relates to the use of the copper-based catalyst described in the first aspect of the present invention for catalyzing the hydrogenation of dimethyl oxalate to generate methyl glycolate. In this application, the yield of methyl glycolate is greater than 70%, preferably greater than 80%, more preferably greater than 90%, even as high as 95%.

Preferably, the dimethyl oxalate is vaporized and mixed with hydrogen before entering the reactor, the mass space velocity of dimethyl oxalate is 0.5-5h ^-1 , the hydrogen ester molar ratio (referred to as hydrogen ester ratio) is 20-150, and the reaction The reaction temperature in the vessel is 160-240° C., and the reaction pressure is 1.5-3.5 MPa.

Compared with the prior art, the present invention has the following beneficial effects:

1. The present invention provides for the first time a copper-based catalyst whose active component is Cu single atoms and/or Cu atom clusters composed of several atoms. The carrier of the copper-based catalyst is silicon dioxide and a substance containing oxygen defects on the surface. The mass ratio of silicon to the substance containing oxygen defects on the surface is 1:(3.6～7.2); the active component of the copper-based catalyst is copper species, and the copper species is Cu single atom and/or Cu composed of several Cu atoms Atomic clusters, the size of the Cu atomic clusters is less than 0.8nm, and based on the total mass of the copper-based catalyst, the loading amount of the copper species is 5%-7%.

2. The present invention firstly prepares silica-loaded copper oxide nanoparticles as the first raw material by the ammonia distillation method, wherein the particle size of the copper oxide nanoparticles in the first raw material is less than 4nm, due to the silica-loaded The particle size of copper oxide nanoparticles is small, so that the copper oxide nanoparticles on the first raw material can be reduced to copper nanoparticles at 200-400 ° C and further migrate to the second raw material to form Cu single atoms and/or several Cu atomic clusters composed of Cu atoms, the lower migration temperature prevents Cu single atoms or Cu atomic clusters from further agglomerating into copper nanoparticles, thereby obtaining the copper-based catalyst of the present invention that supports Cu atomic clusters or Cu single atoms on a mixed carrier.

3. The copper-based catalyst of the present invention has a good effect on the selective hydrogenation of the intermediate product methyl glycolate in the hydrogenation reaction of dimethyl oxalate. Among them, when the _Cu3 cluster composed of three copper atoms is used as the catalyst, the reaction temperature is 200 ° C, the reaction pressure is 2.5 MPa, and when the hydrogen-ester ratio of the feed is 80, the yield of the intermediate product methyl glycolate reaches 95%. When the copper-based catalyst of reported oxide support is used for this reaction, the yield of intermediate product methyl glycolate is only 84%, and the yield of intermediate product methyl glycolate corresponding to noble metal silver-based catalyst can usually reach about 93%, so When the Cu ₃ cluster catalyst of the present invention is used in the reaction, the yield of the intermediate product methyl glycolate far exceeds that of the existing reported copper-based catalyst, and is comparable to that of the noble metal silver-based catalyst. The copper-based catalyst of the present invention can replace the silver-based catalyst and be developed as an industrialized catalyst. The catalyst production cost is greatly saved, and the energy consumption required for product separation is reduced.

4. The excellent stability exhibited by the copper-based catalyst of the present invention in the hydrogenation process of dimethyl oxalate makes the production process of the hydrogenation of dimethyl oxalate used in the present invention to prepare methyl glycolate stable.

Description of drawings

Fig. 1 is the spherical aberration-corrected transmission electron microscope diagram of the copper-based catalyst sample 1 prepared in Example 1 and the DFT simulation diagram of the structure, wherein a diagram is a spherical aberration transmission electron microscope diagram and a contrast signal intensity diagram of S1 and S2 directions, and diagram b It is a partial enlarged view of the box in figure a, and figure c is a DFT simulation figure of the corresponding structure. The copper species of copper-based catalyst sample 1 is a Cu atomic cluster (Cu ₃ ) composed of three copper atoms;

Fig. 2 is the transmission electron microscope picture of the first raw material and the second raw material in the preparation process of embodiment 1 and embodiment 6, wherein a and b picture are the first raw material (the material of copper oxide nanoparticle supported by silicon dioxide) in hydrogen atmosphere Transmission electron micrographs after reduction at 300°C for 4 hours, c and d are transmission electron micrographs of the second raw material (ceria precursor);

3 is a spherical aberration-corrected transmission electron microscope image of the copper-based catalyst sample 2 prepared in Example 3, wherein the copper species of the copper-based catalyst sample 1 is a Cu atomic cluster (Cu ₃₀ ) composed of 30 copper atoms;

Fig. 4 is the X-ray absorption fine structure spectrogram of the copper-based catalyst sample 1-3 and metal copper prepared by embodiment 1-3, cuprous oxide and cupric oxide standard, wherein A is the X-ray absorption near-edge structure spectrogram, B is the derivative function diagram of the X-ray absorption near-edge structure spectrum, and C is the extended X-ray absorption fine structure spectrum;

Fig. 5 is that the copper-based catalyst sample 1-3 prepared by embodiment 1-3 is used in the hydrogenation reaction of dimethyl oxalate, the conversion rate of dimethyl oxalate and ethylene glycol (EG), methyl glycolate (MG) The selectivity results, wherein the reaction conditions are: reaction temperature 200 ℃, reaction pressure 2.5MPa, hydrogen ester ratio 80, dimethyl oxalate mass space velocity 3h ^-1 ;

Fig. 6 is the evaluation result of methyl glycolate produced by hydrogenation of dimethyl oxalate in embodiment 5;

7 is a spherical aberration-corrected transmission electron microscope image and a contrast signal intensity image in the S2 direction of the copper-based catalyst sample 6 prepared in Example 6.

Detailed ways

The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments. It should be noted that: the following examples are illustrative, not restrictive, and the protection scope of the present invention cannot be limited by the following examples. The raw materials needed in the following examples and comparative examples are all commercially available.

Example 1

Preparation of the first raw material (material of silica-loaded copper oxide nanoparticles):

Weigh 18g of copper nitrate trihydrate and add 100mL of deionized water to stir to dissolve, and slowly add 70mL of 28% ammonia water to make cuproammonia solution, and stir evenly at 30°C. Then, 30% silica sol was added dropwise into the solution, and the aging was continued for 4 hours under stirring. Raise the temperature to 80°C to evaporate the ammonia in the solution, and monitor the pH of the solution at any time. When the pH=7, the temperature is lowered, and the process of distilling ammonia stops. The obtained mixed solution was filtered, washed, dried at 80° C., and calcined at 400° C. for 4 hours in an air atmosphere to obtain a material of silica-supported copper oxide nanoparticles.

Preparation of the second raw material (ceria precursor):

Weigh 25g of cerium dioxide hexahydrate, grind it evenly in a mortar, and bake it at 250° C. for 2 hours in an air atmosphere to obtain a ceria precursor.

Figure 2 is a transmission electron microscope image of the first raw material and the second raw material in the preparation process of Example 1, wherein a and b are the first raw material (the material of silica-loaded copper oxide nanoparticles) carried out at 300 ° C in a hydrogen atmosphere Transmission electron micrograph after reduction for 4 hours, c and d are transmission electron micrographs of the second raw material (ceria precursor).

Preparation of copper-based catalyst sample 1:

The silica-supported copper oxide nanoparticles and ceria were mechanically mixed according to a mass ratio of 1:3.6 to obtain a raw material mixture, and then the raw material mixture was subjected to online reduction treatment and heat treatment to obtain copper-based catalyst sample 1.

Copper-based catalyst sample 1 online processing:

The on-line processing of copper-based catalyst sample 1 in this example was carried out in a fixed-bed reactor. Press the raw material mixture without heat treatment into tablets, and sieve it into particles with a size of 40-60 meshes. Weigh 0.58 g and place it in an isothermal reactor, and pass it into a hydrogen atmosphere to carry out reduction at 300 ° C. The reduction time is 4 hours ( first-stage reduction treatment), and then lower the temperature to 200° C. for 100 hours (second-stage reduction treatment), with a hydrogen gas flow rate of 20-150 mL/g, to obtain the copper-based catalyst sample 1 used in the present invention.

The characterization of the copper-based catalyst sample 1 is shown in Figure 1, in which a is a spherical aberration transmission electron microscope image and a contrast signal intensity map in the S1 and S2 directions, b is a partial enlarged view of the box in a, and c is the DFT of the corresponding structure mock diagram. It can be seen that under this angle, the atomic distance of Cu-Cu is 0.20nm, and the distance of Ce-Ce is 0.31nm. Due to the low atomic number of O, it is almost invisible in the spherical aberration transmission electron microscope. And because the atomic number of Ce is greater than the atomic number of Cu, it can also be clearly found through the signal intensities in the S1 and S2 directions that the existence form of copper species on the surface of cerium oxide is roughly 3 Cu atomic clusters, so the obtained in this embodiment The copper-based catalyst sample 1 is abbreviated as Cu ₃ .

Example 2-3

Examples 2-3 The copper-based catalyst samples 2-3 were prepared by controlling the mass percentage of copper in the silica-supported copper oxide nanoparticles to control the size of the copper species in the copper-based catalyst. The specific preparation conditions are shown in Table 1, and the experimental conditions not shown in Table 1 are the same as those in Example 1.

Table 1 Effect of different copper nitrate additions on copper species in copper-based catalysts

The spherical aberration-corrected transmission electron microscope of the copper-based catalyst sample 3 is shown in FIG. 3 .

It can be seen from Figure 3 that the copper oxide nanoparticles supported on the silica were reduced to copper nanoparticles, and the copper nanoparticles successfully migrated to the cerium oxide to form Cu clusters composed of thirty copper atoms. Catalyst sample 3 is abbreviated as Cu ₃₀ .

Meanwhile, Fig. 4 is the X-ray absorption fine structure spectrum of copper-based catalyst sample 1-3, wherein A is the X-ray absorption near-edge structure spectrum (XANES figure), and B is the derivative function of the X-ray absorption near-edge structure spectrum Figure C is the extended X-ray absorption fine structure spectrum (EXASF figure), in which the peak of the Cu-O bond is at the atomic distance of 1.85 angstroms, and the peak of the Cu-Cu bond is at the atomic distance of 2.53 angstroms. From the XANES diagram of copper in Figure 4, it can be proved that the average valence state of this Cu atomic cluster is between 0 and +1; since there are only Cu-O bond peaks in the Cu element EXAFS diagram, there is no Cu-Cu bond peak, It can be illustrated that the existence form of Cu species in the catalyst of Example 2 is a single atom; because the peak of the Cu-Cu bond in the Cu element EXAFS figure in the sample of Example 1 is very weak, by fitting its coordination number is 2.6, it can be illustrated that the embodiment The copper species in 1 is a Cu cluster composed of 2-3 Cu atoms; since the peak of the Cu-Cu bond in the EXAFS diagram of the Cu element in the sample of Example 3 is weak, by fitting its coordination number to 4.8, it can be obtained by calculation The copper species in Example 3 exists in the form of 0.8 nm Cu clusters.

Example 4

In this example, the gas-phase hydrogenation reaction of dimethyl oxalate was carried out in a fixed-bed reactor. Press copper-based catalyst samples 1-3 into tablets, and sieve them into particles with a size of 40-60 meshes. Weigh 0.58 g and place them in an isothermal reactor. It is mixed with hydrogen and enters the reaction tube, the hydrogen-to-ester ratio is 80, the mass space velocity of dimethyl oxalate is 3h ^-1 , and the reaction is carried out at 2.5MPa. Analyze the product by gas chromatography to obtain the components of dimethyl oxalate (DMO), ethylene glycol (EG), methyl glycolate (MG) and ethanol (EtOH). The conversion rate of dimethyl ester and the selectivity of ethylene glycol (EG) and methyl glycolate (MG). The conversion rate of dimethyl oxalate and the selectivity results of ethylene glycol (EG) and methyl glycolate (MG) are shown in Figure 4.

It can be seen from Figure 5 that with the increase of the size of Cu clusters in the copper-based catalyst, the selectivity of the intermediate product methyl glycolate (MG) decreases, while the selectivity of ethylene glycol (EG) increases. The _Cu3 cluster composed of three copper atoms was used as a catalyst (copper-based catalyst sample 1) in the hydrogenation reaction of dimethyl oxalate at a reaction temperature of 200 °C, a reaction pressure of 2.5 MPa, and a feed ratio of hydrogen to ester of 80 , the yield of the intermediate product methyl glycolate reaches 95%, far exceeding the existing reported copper-based catalysts, and comparable to the catalytic activity of noble metal silver-based catalysts.

Example 5

The catalyst precursor and mixing means of this embodiment are the same as in Example 1, but in the online processing process, only the catalyst is reduced at 300°C for 4 hours, and it is not heat treated at 200°C for 100 hours, but directly at 200°C The hydrogenation reaction of oxalate was evaluated. Evaluation conditions are the same as in Example 1. Through this embodiment, the influence of the atomic migration phenomenon of copper nanoparticles on the hydrogenation reaction performance of oxalate can be observed during the evaluation process, and its stability can be tested. The specific results are shown in Figure 6.

Due to the reduction at 300 °C and 4 hours before the reaction, the copper oxide nanoparticles supported on the silica were reduced to copper nanoparticles. It can be seen from Figure 6 that the copper species in the catalyst in the early stage of the reaction existed in the form of copper nanoparticles. The product selectivity of its catalyzed hydrogenation of oxalate is mainly ethylene glycol, and the yield of methyl glycolate is extremely low; as the reaction time prolongs, since the reaction is in a non-oxidizing atmosphere at 200 ° C, the di The copper nanoparticles loaded on the silica gradually migrate to the cerium oxide to form a Cu atom cluster composed of 2-3 copper atoms, which catalyzes the hydrogenation of oxalate from ethylene glycol to methyl glycolate, and finally A methyl glycolate yield of up to 95% is obtained, and the structure of the copper atom cluster can be kept stable, thereby obtaining a stable methyl glycolate yield.

Example 6

This embodiment is the preparation of copper-based catalyst sample 4:

The preparation method of the first raw material and the second raw material is the same as in Example 1, and then the first raw material is subjected to the first-stage reduction treatment, and then mixed with the second raw material, and then the second-stage reduction treatment is carried out after mixing to obtain a copper-based Catalyst sample 4, specifically: first place the first raw material in an isothermal reactor, pass it into a hydrogen atmosphere for reduction at 300°C, and the reduction time is 4 hours, then mix it with the second raw material, and then mix it under a nitrogen atmosphere Keep at 200°C for 100 hours; the hydrogen flow rate in the first stage is 20-150mL/g, and the nitrogen flow rate in the second stage is 10-200mL/g.

The spherical aberration-corrected transmission electron microscope of copper-based catalyst sample 4 is shown in Figure 7. It can be seen that, similar to Figure 1 of copper-based catalyst sample 4, the copper oxide nanoparticles supported on silica are reduced to copper nanoparticles, and the copper nanoparticles Successfully migrated to cerium oxide to form a Cu atomic cluster composed of three copper atoms, so the preparation method can also obtain the copper-based catalyst in which the copper species described in the present invention is a Cu atomic cluster composed of several Cu atoms.

The present invention has been described as an example above, and it should be noted that, without departing from the core of the present invention, any simple deformation, modification or other equivalent replacements that can be made by those skilled in the art without creative labor all fall within the scope of this invention. protection scope of the invention.

Claims (6)

1. The copper-based catalyst loaded with Cu atom clusters or Cu monoatoms by a mixed carrier is characterized by comprising a carrier and an active component, wherein the carrier is silicon dioxide and substances with surface oxygen defects, and the mass ratio of the silicon oxide to the substances with surface oxygen defects is 1 (3.6-7.2); the active component is a copper species, the copper species is Cu atom clusters composed of Cu monoatoms and/or Cu atoms, the Cu atom clusters are smaller than 0.8nm in size, and the loading amount of the copper species is 5% -7% based on the total mass of the copper-based catalyst.

2. The copper-based catalyst according to claim 1, wherein the surface oxygen-containing defective material is a surface oxygen-containing defective metal oxide selected from the group consisting of cerium oxide, zinc oxide, zirconium oxide, titanium oxide, and manganese oxide.

3. The copper-based catalyst according to claim 1, wherein the silica has a layered structure, and the surface oxygen-containing defect substance has a particle diameter of 4.0nm to 20.0nm.

4. The copper-based catalyst according to claim 1, wherein the average valence of copper in the copper species is 0 to 1.

5. Copper-based catalyst according to claim 1, characterized in that the number of Cu atoms in the Cu clusters is less than 100, preferably less than 60, more preferably less than 30, still more preferably less than 15, still more preferably less than 6, most preferably less than 3.

6. Use of the copper-based catalyst of claim 1 for catalyzing the selective hydrogenation of dimethyl oxalate to methyl glycolate.

Images