Binary single-site materials for controlling active site spatial distribution, methods of making and use

Abstract

The application discloses a kind of binary unit point material of controlling active site spatial distribution, preparation method and application, the binary unit point material includes SiO2 Nanosphere, unit point metal encapsulated in SiO2 Nanosphere inside and unit point metal anchored in SiO2 Nanosphere surface;Wherein the unit point metal includes at least one of Cu, Zr, Yb, Hf, Y and Zn.The preparation method using reverse microemulsion method has universality, by changing the type of coated organic metal salt, can synthesize the high dispersion unit point catalyst of corresponding metal, solves the problem that high dispersion single metal site cannot be synthesized in SiO2 Body phase, also can accurately control the spatial distribution of active site, and the catalyst inhibits byproduct ethylene generation, by ordered catalytic cascade reaction, significantly improve catalytic activity and butene selectivity, can better satisfy ethanol preparation olefin catalysis field.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically relating to a binary unit site material for controlling the spatial distribution of active sites, its preparation method, and its application. Background Technology

[0002] Single-atom catalysts are defined as monodisperse metal atoms stabilized on a support. They offer advantages such as maximized atomic efficiency and well-defined structures, and provide a state-of-the-art platform for understanding the structure-activity relationship of catalysts, thus attracting extensive research. Various studies focus on altering the local environment of individual active sites to improve the catalytic performance of single-atom catalysts.

[0003] Recently, two isolated metal atoms located close to each other have been developed as diatomic catalysts. The synergistic effect of the two single-atom sites can enhance catalytic performance by adjusting the activation and adsorption / desorption structures of reactants or intermediates. However, apart from simple model reactions, most industrial catalytic processes require bifunctional or multifunctional catalysts. However, due to the limited consistency of catalytic functions, most single-atom and diatomic catalysts do not adequately meet these requirements.

[0004] Introducing multiple active sites to catalyze corresponding reaction steps, organizing various catalysts into dual-bed, triple-bed, or physical mixture configurations is an effective strategy for complex reactions. For example, reference 1 (Selective conversion of syngas to light olefins, Science, 2016, 351(6277), 1065-1068.) describes a catalyst with two functional groups packed in different modes (separate or mixed), which separates CO activation and CC coupling to two different types of active sites. CO and H2 partially reduce oxides (ZnCrO2). x The surface is activated, while CC coupling is controlled in the closed environment of zeolite (MSAPO).

[0005] In more complex cases, such as reference 2 (Single-pass transformation of syngas into ethanol with high selectivity by triple tandem catalysis, Nat. Commun, 2020, 11, 827.), a highly efficient trifunctional tandem system consisting of potassium-modified ZnO-ZrO2, modified mordenite, and Pt-Sn / SiC is provided. This system operates compatibly in a single reactor for the conversion of syngas into ethanol. This work proposes an efficient method to decouple complex, uncontrollable reactions based on a single catalyst into multiple steps in tandem.

[0006] However, both physical mixing and multi-bed packed tandem catalysts have inherent limitations, which prevent the catalytic steps from proceeding in an orderly manner in complex reactions. During catalysis, active sites are randomly distributed and simultaneously exposed to reactants, causing reactants to interact with various active sites in a random rather than controlled order, resulting in significant side reactions and a substantial reduction in the selectivity of the target product.

[0007] Therefore, materials must be processed into the desired structure to precisely control the spatial distribution of active sites, thereby promoting complex reactions to proceed in a predetermined sequence and catalyzing complex cascade reactions. Summary of the Invention

[0008] In view of the shortcomings of the prior art, the present invention provides a binary unit site material for controlling the spatial distribution of active sites, a preparation method and an application. The binary unit site material precisely controls the spatial distribution of active sites, promotes complex reactions to proceed in a predetermined order, catalyzes complex cascade reactions, and significantly improves the activity and selectivity of the catalyst.

[0009] The present invention provides a binary unit point material for controlling the spatial distribution of active sites, comprising SiO2 nanospheres, unit point metal encapsulated inside the SiO2 nanospheres, and unit point metal anchored on the surface of the SiO2 nanospheres; wherein the unit point metal comprises at least one of Cu, Zr, Yb, Hf, Y, and Zn.

[0010] The binary unit-point material provided by this invention encapsulates a unit-point metal for dehydration and aldol condensation within the bulk phase of SiO2 nanospheres. Metal doping partially disrupts the tetrahedral structure of SiO2 and increases the disorder of atomic arrangement, generating defects. Based on these defects, another unit-point metal is constructed and anchored to the surface of the SiO2 nanospheres for dehydrogenation, thereby synthesizing a binary unit-point material with a specific spatial distribution of active sites. This specific spatial distribution of active sites promotes complex reactions to proceed in a predetermined sequence, allowing reactants to first contact the dehydrogenation sites to form intermediates, and then contact the active sites within the bulk phase to undergo aldol condensation and dehydration. This catalyzes complex cascade reactions, inhibits the formation of byproducts, and significantly improves the activity and selectivity of the catalyst.

[0011] Preferably, the diameter of the SiO2 nanospheres is 20 nm to 30 nm.

[0012] Preferably, the molar ratio of the unit point metal to the SiO2 nanospheres is 0–1.14:0–30.58, and the molar number of the unit point metal and the SiO2 nanospheres is not 0.

[0013] More preferably, the molar ratio of the unit point metal to the SiO2 nanospheres is 0.01–1.14:0.01–30.58.

[0014] On the other hand, the present invention also innovatively provides a method for preparing the aforementioned binary unit point material, comprising the following steps:

[0015] (1) A precursor solution was prepared by reverse microemulsion method using alkane organic solvent, surfactant, ammonia, acetylacetone metal salt 1 and silicon source. After centrifugation, washing and drying, the precursor solution was calcined to prepare SiO2 catalyst encapsulated with unit point metal.

[0016] (2) Using the impregnation method, acetylacetone metal salt 2 is impregnated onto the SiO2 catalyst encapsulated with unit point metal. After centrifugation, washing and drying, it is calcined to obtain binary unit point material, which is a binary catalyst with a specific spatial distribution of active sites.

[0017] This invention directly encapsulates organometallic salts within SiO2 nanospheres using a reverse microemulsion method. Through calcination and vaporization, the encapsulated organometallic salts within the SiO2 bulk phase are transformed into highly dispersed unit-point metals. The encapsulated metal sites are primarily embedded within the SiO2 bulk phase, rather than on the surface. The entry of the unit-point metals into the SiO2 bulk phase partially disrupts the tetrahedral structure of SiO2 and increases the disorder of atomic arrangement, generating defects. These defects are then utilized to construct another highly dispersed unit-point metal, anchoring it to the material surface, thereby synthesizing a binary unit-point material with precisely controlled spatial distribution of active sites.

[0018] Preferably, the alkane organic solvent mentioned in step (1) is cyclohexane, n-hexane, or dodecane.

[0019] In the reverse microemulsion method, alkane organic solvents are usually used as the oil phase (continuous phase) to encapsulate aqueous droplets to form a stable microemulsion system. These alkane organic solvents have the characteristics of low polarity and immiscibility with water, which can flexibly adapt to different reaction conditions. At the same time, they can synergistically form a stable interfacial film with surfactants to ensure the uniformity and controllability of the microemulsion during the synthesis of nanocatalysts.

[0020] More preferably, the alkane organic solvent is cyclohexane.

[0021] Preferably, the surfactant mentioned in step (1) is a nonionic surfactant, including polyoxyethylene (9) nonylphenyl ether, alkylphenol polyoxyethylene ether, or Tween.

[0022] The surfactants mentioned above are low in toxicity, environmentally friendly and biodegradable, highly stable over a wide pH range, and can be flexibly adapted to the emulsification requirements of different oil phases by adjusting the number of ethylene oxides or the chain length, forming stable microemulsion droplets.

[0023] More preferably, the surfactant mentioned in step (1) is polyoxyethylene (9) nonylphenyl ether.

[0024] More preferably, the mass ratio of the alkane organic solvent to the surfactant in step (1) is 0-77.9:0-16.9.

[0025] Preferably, the acetylacetone metal salt 1 and acetylacetone metal salt 2 are at least one of copper acetylacetone, zirconium acetylacetone, ytterbium acetylacetone, hafnium acetylacetone, yttrium acetylacetone, and zinc acetylacetone.

[0026] Choosing the above-mentioned acetylacetone metal salt as a metal precursor provides excellent oil-phase solubility (highly compatible with alkane organic solvents), controllable thermal decomposition characteristics (precisely regulating the nucleation and growth of nanocatalysts), and strong coordination stabilization (inhibiting metal particle aggregation). Furthermore, its volatile byproducts after decomposition can reduce impurity residues, ensuring high purity and excellent performance of the catalyst, while also being suitable for the catalytic system of ethanol to butene production.

[0027] Preferably, the molar ratio of acetylacetone metal salt 1 to acetylacetone metal salt 2 is 0-0.66:0-0.48, and the molar number of both acetylacetone metal salt 1 and acetylacetone metal salt 2 is not 0.

[0028] More preferably, the molar ratio of acetylacetone metal salt 1 to acetylacetone metal salt 2 is 0.01-0.66:0.01-0.48.

[0029] Preferably, the molar ratio of acetylacetone metal salt to silicon source is 0-1.14:0-30.58, and the number of moles of acetylacetone metal salt and silicon source is not 0, wherein the acetylacetone metal salt includes acetylacetone metal salt 1 and acetylacetone metal salt 2.

[0030] More preferably, the molar ratio of acetylacetone metal salt to silicon source is 0.01–1.14:0.01–30.58.

[0031] Preferably, the silicon source is tetramethoxysilane and octadecyltrimethoxysilane.

[0032] More preferably, the molar ratio of the tetramethoxysilane and octadecyltrimethoxysilane is 0–26.34:0–4.24.

[0033] More preferably, the molar ratio of the tetramethoxysilane and octadecyltrimethoxysilane is 0.01–26.34:0.01–4.24.

[0034] Preferably, the calcination temperature in steps (1) and (2) is 400℃~1000℃, and the holding time is 0.5h~15h.

[0035] The design incorporates suitable calcination temperatures and holding times for the precursors, effectively removing organic matter, moisture, and other volatile impurities from the raw materials. This process vaporizes the organometallic salts encapsulated in the SiO2 bulk phase into highly dispersed unit-point metals, resulting in binary unit-point materials encapsulated internally and anchored externally within SiO2 nanospheres. This ensures that in the ethanol-to-butene reaction, the reactant ethanol first contacts the externally anchored dehydrogenation sites, generating the important intermediate acetaldehyde. This inhibits the dehydration of ethanol to produce the byproduct ethylene. Then, it contacts the dehydration sites within the SiO2 nanospheres, where aldol condensation and dehydration produce crotonaldehyde. This achieves an ordered catalytic complex cascade reaction, facilitating the efficient one-step catalytic production of butene from ethanol.

[0036] More preferably, the calcination atmosphere described in steps (1) and (2) is air.

[0037] This invention also provides the application of the aforementioned binary unit point material in the field of ethanol-to-olefins catalysis.

[0038] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0039] (1) The binary unit site material with a specific spatial distribution of active sites prepared in this invention encapsulates dehydration and aldol condensation sites in the SiO2 bulk phase and anchors dehydrogenation sites on the SiO2 surface. This binary unit site material can achieve ordered catalytic complex cascade reaction in the ethanol to butene reaction, so that the reactant ethanol first contacts the dehydrogenation site to generate the important intermediate acetaldehyde, thereby inhibiting the dehydration of ethanol to generate the byproduct ethylene. Then, it contacts the dehydration site in the SiO2 bulk phase, and the aldol condenses and dehydrates to generate crotonaldehyde. By precisely controlling the spatial distribution of active sites, it is beneficial to improve the selectivity of the target product butene.

[0040] (2) The reverse microemulsion method provided by the present invention has universality. It synthesizes SiO2-coated organometal salt precursors by directly coating organometal salts, and then encapsulates the unit metal sites in the SiO2 bulk phase by high-temperature calcination, thus solving the technical problem that it is impossible to synthesize highly dispersed single metal sites in the SiO2 bulk phase. Attached Figure Description

[0041] Figure 1 The design concept of the binary unit point material (Cu1-Zr1@SiO2) provided in the embodiments of the present invention.

[0042] Figure 2 Aberration-corrected high-angle annular dark-field scanning transmission electron microscope and its energy spectrum of Zr element of the zirconium-doped catalyst (Zr1@SiO2) provided in the embodiments of the present invention.

[0043] Figure 3 Cu provided for embodiments of the present invention i -Aberration-corrected high-angle annular dark-field scanning transmission electron microscope image of Zr1@SiO2 and its Cu element energy spectrum.

[0044] Figure 4 The energy spectrum of Zr element in Cu1-Zr1@SiO2 provided in an embodiment of the present invention.

[0045] Figure 5 A high-angle annular dark-field scanning electron microscope with spherical aberration correction for Cu1-Zr1@SiO2 provided in an embodiment of the present invention.

[0046] Figure 6 for Figure 3 Electron energy loss spectrum of the orange region in Cu1-Zr1@SiO2.

[0047] Figure 7 This is a low-energy ion scattering depth profile of Cu1-Zr1@SiO2 provided in an embodiment of the present invention.

[0048] Figure 8 for Figure 7 A magnified view of a low-energy ion scattering depth profile with the vertical axis ranging from 0 to 1.5.

[0049] Figure 9 The catalysts provided in the embodiments and comparative examples of the present invention are used to catalyze the one-step production of butene from ethanol, thereby increasing the ethanol conversion rate.

[0050] Figure 10 The catalysts provided in the embodiments and comparative examples of the present invention are used to improve the selectivity of ethylene, acetaldehyde and butene in the one-step ethanol-to-butene reaction.

[0051] Figure 11 The catalysts provided in the embodiments and comparative examples of this invention are used in the reaction of ethanol to butene in a one-step process, C 3+ Selectivity of olefins. Detailed Implementation

[0052] To more clearly illustrate the objectives, technical solutions, and advantages of this invention, the following detailed description will be provided in conjunction with embodiments. Please note that these embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Modifications or equivalent substitutions made by those skilled in the art based on their understanding of the technical solutions of this invention are all within the protection scope of this invention.

[0053] The raw materials were purchased from the market.

[0054] Example 1

[0055] Example 1 of this invention provides a method for preparing a binary unit point material (Cu1-Zr1@SiO2), the specific steps of which are as follows:

[0056] (1) Preparation of zirconium-doped catalyst (Zr1@SiO2) by reverse microemulsion method (RMM): 50 mL of cyclohexane and 16 mL of... CO-630 (polyoxyethylene (9) nonylphenyl ether) and 2.0 mL of ammonia solution were mixed in a three-necked flask and stirred for 10 min. Then, a mixture containing 50 mL of cyclohexane, 0.66 mmol of tetra(acetylacetone)zirconium (IV) (Zr(acac)4), 2.0 mL of tetramethoxysilane (TMOS, 98%), and 2.0 mL of octadecyltrimethoxysilane (C18TMS, 90%) was added. After stirring at 30 °C for 1 h, the solid product was separated by centrifugation and thoroughly washed with ethanol. The sample was dried at 80 °C for 10 h and then calcined in air at 400 °C for 2 h, denoted as Zr1@SiO2.

[0057] (2) 0.77 g of Zr1@SiO2 was dispersed in 75 mL of ultrapure water, and 0.24 mmol of copper acetylacetonate (II) was dispersed in 20 mL of ultrapure water and sonicated for 10 min. The metal precursor solution was added dropwise to the Zr1@SiO2 dispersion at 1000 rpm. After stirring for 10 h, the product was collected by centrifugation and washed twice with water. Subsequently, the centrifuged product was dried at 60 °C and calcined in a muffle furnace at 400 °C for 2 h. The resulting sample was named Cu1-Zr1@SiO2.

[0058] Figure 1 As shown in the schematic diagram, a binary unit site catalyst Cu1-Zr1@SiO2 with a specific spatial arrangement was synthesized via a reverse microemulsion method. This catalyst consists of non-bridging oxygen hole centers generated by Zr doping into SiO2, anchoring the unit sites Cu. Specifically, an organometallic salt is first encapsulated in SiO2 nanospheres. After high-temperature calcination in air, the organometallic precursor vaporizes and transforms into monodisperse centers within the SiO2 bulk phase. Then, the defects generated by doping are used to anchor the unit sites Cu. The outermost surface of the synthesized binary unit site catalyst mainly contains unit sites Cu, while Zr species are mainly dispersed within the SiO2 bulk phase.

[0059] like Figure 2 As shown, aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC-HAADF-STEM) and energy dispersive spectroscopy (EDS) confirm that Zr species in Zr1@SiO2 are mainly encapsulated within the SiO2 bulk phase, rather than on the surface. Combined with... Figures 3-5The Cu and Zr species were found to be dispersed at unit points in Cu1-Zr1@SiO2. Further analysis using electron energy loss spectroscopy (EELS) and low-energy particle scattering (LEIS) was used to characterize the spatial distribution of elements in Cu1-Zr1@SiO2. Figure 6 EELS confirmed that Zr sites are mainly distributed in the bulk phase of Cu1-Zr1@SiO2. Figure 7 and Figure 8 The depth profile results show that the Cu signal decreases with increasing depth, while the Zr signal gradually increases with increasing depth. LEIS analysis results indicate that Cu is enriched on the SiO2 surface, with a small amount of Cu distributed in the bulk phase, while Zr is only distributed in the Cu1-Zr1@SiO2 bulk phase.

[0060] Example 2

[0061] The preparation process of Example 2 is the same as that of Example 1, except that the molar amount of copper acetylacetonate (II) introduced is 0.48 mmol, that is, the molar ratio of tetrazirconium tetra(acetylacetonate) (IV) and copper acetylacetonate (II) is different.

[0062] Example 3

[0063] The preparation process of Example 3 is the same as that of Example 1, except that the amount of tetramethoxysilane introduced is 4 mL, that is, the molar ratio of acetylacetone metal salt and silicon source is different.

[0064] Example 4

[0065] The preparation process of Example 4 is the same as that of Example 1, except that the calcination temperature is 1000℃ and the holding time is 6h.

[0066] Comparative Example 1

[0067] Using an impregnation method, 0.69 g of SiO2 was dispersed in 75 mL of ultrapure water, while 0.24 mmol of copper acetylacetonate(II) (Cu(acac)2) and 0.66 mmol of zirconium acetylacetonate(IV) were dispersed in 20 mL of ultrapure water, and the mixture was sonicated for 10 min. The metal precursor solution was then added dropwise to the SiO2-dispersed solution under stirring at 1000 rpm. After stirring for 10 h, the product was collected by centrifugation and washed twice with water. Subsequently, the centrifuged product was dried at 60 °C and calcined in a muffle furnace at 400 °C for 2 h. The resulting sample was named CuZr / SiO2.

[0068] Comparative Example 2

[0069] 0.77 g of SiO2 was dispersed in 75 mL of ultrapure water, and 0.24 mmol of copper(II) acetylacetonate was dispersed in 20 mL of ultrapure water and sonicated for 10 min. The metal precursor solution was added dropwise to the Zr1@SiO2 dispersion solution at 1000 rpm. After stirring for 10 h, the product was collected by centrifugation and washed twice with water. Subsequently, the centrifuged product was dried at 60 °C and calcined in a muffle furnace at 400 °C for 2 h. The resulting sample was named Cu / SiO2.

[0070] Comparative Example 3

[0071] Preparation of zirconium-doped catalyst (Zr1@SiO2) via reverse microemulsion (RMM): 50 mL of cyclohexane and 16 mL of... O-630 (polyoxyethylene (9) nonylphenyl ether) and 2.0 mL of ammonia solution were mixed in a three-necked flask and stirred for 10 min. Then, a mixture containing 50 mL of cyclohexane, 0.66 mmol of tetra(acetylacetone)zirconium (IV) (Zr(acac)4), 2.0 mL of tetramethoxysilane (TMOS, 98%), and 2.0 mL of octadecyltrimethoxysilane (C18TMS, 90%) was added. After stirring at 30 °C for 1 h, the solid product was separated by centrifugation and thoroughly washed with ethanol. The sample was dried at 80 °C for 10 h and then calcined in air at 400 °C for 2 h, denoted as Zr1@SiO2.

[0072] To investigate the unique role of binary unit site catalysts with specific spatial arrangements in cascade reactions, the above examples and comparative examples were used for catalytic testing of the reaction of ethanol to butene. Reaction conditions: 643 K, 7.8 kPa ethanol, 93.5 kPa H2, weight hourly space velocity (WHSV) = 0.3 h⁻¹. 1 .

[0073] like Figures 9-11 As shown in Table 1, the ethanol conversion rate was determined under the same reaction conditions. As can be seen from Table 1, the ethanol conversion rate of Cu1-Zr1@SiO2 was as high as 95.7%, while that of Cu / SiO2 and CuZr / SiO2 was 84.4%-85.7%, both significantly higher than that of Zr1@SiO2 (46.3%). For Cu / SiO2, acetaldehyde was the main product with a selectivity of up to 95.1%, and no large amount of butene was formed. This is because Cu mainly acts as the ethanol dehydrogenation site and lacks aldol condensation sites. On the other hand, for Zr1@SiO2, ethylene was the main product because Zr acts as the ethanol dehydration site. It is noteworthy that compared to CuZr / SiO2, Cu1-Zr1@SiO2 had a much lower selectivity for ethylene, and the conversion rates of butene and C were significantly lower. 3+The significantly improved selectivity for olefins indicates that binary unit site catalysts with specific spatial distributions have unique advantages for the ethanol-to-butene reaction.

[0074] Table 1 Catalytic performance tests of the examples and comparative examples

[0075]

Claims

1. A binary unit point material for controlling the spatial distribution of active sites, characterized in that, It includes SiO2 nanospheres, unit points of Zr encapsulated inside the SiO2 nanospheres, and unit points of Cu anchored on the surface of the SiO2 nanospheres.

2. The binary unit point material according to claim 1, characterized in that, The diameter of the SiO2 nanospheres is 20 nm to 30 nm.

3. The binary unit point material according to claim 1, characterized in that, The molar ratio of the unit point Zr, unit point Cu and SiO2 nanospheres is 0~1.14:0~30.58, and the molar number of the unit point Zr, unit point Cu and SiO2 nanospheres is not 0.

4. A method for preparing a binary unit point material according to any one of claims 1-3, characterized in that, Includes the following steps: (1) A precursor solution was prepared by using a reverse microemulsion method with alkane organic solvent, surfactant, ammonia, zirconium acetylacetonate and silicon source. After centrifugation, washing and drying, the precursor solution was calcined to prepare SiO2 catalyst encapsulated with unit point metal. (2) The copper acetylacetone was impregnated onto the SiO2 sample containing the unit point metal by the impregnation method. After centrifugation, washing and drying, the sample was calcined to obtain the binary unit point material.

5. The preparation method according to claim 4, characterized in that, The alkane organic solvent mentioned in step (1) is cyclohexane, n-hexane, or dodecane.

6. The preparation method according to claim 4, characterized in that, The mass ratio of alkane organic solvent to surfactant in step (1) is 0~77.9:0~16.

9.

7. The preparation method according to claim 4, characterized in that, The molar ratio of zirconium acetylacetonate to copper acetylacetonate is 0~0.66:0~0.48, and the molar number of both zirconium acetylacetonate and copper acetylacetonate is not 0.

8. The preparation method according to claim 4, characterized in that, The silicon source is tetramethoxysilane and octadecyltrimethoxysilane; The molar ratio of the tetramethoxysilane to the octadecyltrimethoxysilane is 0~26.34:0~4.

24.

9. The preparation method according to claim 4, characterized in that, The calcination temperature in steps (1) and (2) is 400 ℃~1000 ℃, and the holding time is 0.5 h~15 h.

10. The application of the binary unit point material according to any one of claims 1-3 in the field of ethanol-to-olefins catalysis.

Images