Gold-rhodium heterostructure catalyst as well as preparation method and application thereof

Abstract

The invention discloses a gold-rhodium heterostructure catalyst and a preparation method and application thereof.The catalyst is of a hamburger-shaped structure and is composed of a carrier and metal particles loaded on the carrier, the metal particles are of a metastable-state gold-rhodium core-shell heterostructure, gold atoms form a shell layer outside the metal particles, and the shell layer is a shell layer outside the metal particles. Rhodium atoms are embedded into an interface between gold atoms and a carrier in a high-temperature reduction mode, and the rhodium atoms form an electronic fence effect region at the interface. The effect can effectively regulate and control the electronic state of gold, and Au can be converted into an Au-state from an Au < m + > state, so that molecular oxygen is remarkably activated, side reactions are inhibited, and the catalytic activity of hydrocarbon selective oxidation reaction is remarkably improved on the premise that selectivity is not affected. In addition, the gold-rhodium heterostructure catalyst also shows excellent stability. The preparation method of the catalyst is simple and easy to implement, has relatively strong controllability, is suitable for selective oxidation reaction of various hydrocarbons, and shows a wide industrial application prospect.

Description

Technical Field

[0001] The present invention belongs to the field of catalytic materials, and particularly relates to a gold-rhodium heterostructure catalyst, a preparation method thereof, and an application thereof in the selective oxidation reaction of hydrocarbons. Background Art

[0002] Selective oxidation reactions play an extremely important role in current chemical industrial processes. Among them, the propylene epoxidation reaction to produce propylene oxide and the propane oxidation reaction to produce acetone have great industrial value. In recent years, supported gold catalysts (such as Au / TS-1) have attracted much attention in selective oxidation reactions due to their unique anti-overoxidation ability. However, due to the weak adsorption and activation ability of Au surface to oxygen and the insufficient dissociation ability of the Au-Ti interface to H2, there are still bottlenecks in the reaction rate and selectivity of this system (J. Catal. 2014, 313, 104 - 112). In order to improve the catalytic performance and reduce the amount of gold used, researchers usually adopt the strategy of gold-based bimetallic catalysts. Compared with relatively inert gold, other transition metals (such as Pt, Pd, Ag) significantly enhance the adsorption and dissociation ability of the catalyst surface to H2 or O2 (Appl. Surf. Sci. 2022, 606, 154834; Appl. Catal. A Gen. 2021, 615, 118060). However, this type of bimetallic catalyst, especially alloy catalysts, is prone to cause over-hydrogenation of olefins to form alkanes or over-oxidation to form CO2 (J. Catal. 2008, 258, 187 - 198; J. Catal. 2011, 281, 12 - 20). Therefore, the development of highly catalytically active gold-based bimetallic catalysts without affecting selectivity remains a major challenge.

[0003] It is generally believed that alloys formed by immiscible metals have poor catalytic application effects due to their easy phase separation and limited interfacial contact (J. Am. Chem. Soc. 2024, 146, 19986–19997). However, with the development of nanotechnology and materials science, it has been found that when the particle size of immiscible alloys is reduced to the nanoscale, the boundary between atomic-scale homogeneity and heterogeneity gradually becomes blurred, and structures such as solid solutions, heterostructures, and intermetallic compounds can be formed (Nano Res. 2023, 16, 9968–9976; Science 2019, 363, 959–964). This type of metastable heterostructure has the characteristics of non-equilibrium state and high energy. Gold element has significant immiscible characteristics and is an ideal material for constructing such heterostructures. At present, there are few reports on the application of heterostructure gold-based catalysts in selective oxidation reactions (Langmuir 2013, 29, 6025–6031; Sci. Rep. 2015, 5, 09849). Summary of the Invention

[0004] The object of the present invention is to solve the bottleneck problems existing in the existing gold-based catalysts, such as weak molecular oxygen activation ability, the activity-selectivity contradiction in the bimetallic system during the selective oxidation reaction, and poor structural stability. After extensive and in-depth research, the inventors of this case found that by designing a heterostructured gold-based catalyst, while retaining the advantages of the gold-based catalyst in selective oxidation, its performance can be further improved, the metal utilization rate can be effectively increased, and the catalyst development cost can be reduced, which is of great significance for developing high-performance and high-stability catalysts required by the industry.

[0005] On this basis, the inventors of this case proposed a gold-rhodium heterostructure catalyst and its preparation method and application. By introducing Rh at the interface between Au and the support to construct an electron fence, the electron density of Au is increased, and Au is changed from the Au m+ state to the Au n- state, which can effectively activate molecular oxygen and at the same time inhibit the occurrence of side reactions, significantly improving the activity of the selective oxidation reaction without affecting the selectivity.

[0006] To achieve the above object, the present invention adopts the following technical solutions:

[0007] In the first aspect of the present invention, it is to provide a gold-rhodium heterostructure catalyst, which has a "hamburger" structure, including a support and metal particles loaded on the support. The metal particles have a metastable gold-rhodium core-shell heterostructure, wherein the gold nanoparticles form the outer shell layer of the metal particles, and rhodium atoms are embedded in the interface between the gold nanoparticles and the support to form an electron fence.

[0008] The present invention is further configured such that the average particle size of the gold nanoparticles is less than 10 nm, preferably 1-5 nm.

[0009] The present invention is further configured such that the support is a titanium-containing material commonly used in the art, including but not limited to TiO2, uncalcined titanium silicalite TS-1-B with micropores blocked by a template agent, and uncalcined titanium silicalite TS-2-B composed of nanoparticle accumulation. The support is preferably uncalcined titanium silicalite TS-1-B with micropores blocked by a template agent.

[0010] In the second aspect of the present invention, it is to provide a preparation method of a gold-rhodium heterostructure catalyst, and the method includes the following steps:

[0011] (1) Loading a gold precursor solution and a rhodium precursor solution on a titanium-containing support;

[0012] (2) Performing high-temperature heat treatment under a certain atmosphere.

[0013] The present invention is further configured such that in the step (1):

[0014] The feeding amounts of the gold precursor solution and the rhodium precursor solution are set according to the gold-rhodium molar ratio, and the gold-rhodium molar ratio is 10:(0.1 - 2.5), preferably 10:(0.5 - 1.5).

[0015] The present invention is further configured such that in step (1):

[0016] The gold precursor is commonly used in the art, such as but not limited to chloroauric acid, sodium thiosulfogoldate, gold hydroxide, etc., and preferably chloroauric acid;

[0017] The rhodium precursor is commonly used in the art, including but not limited to rhodium chloride, rhodium nitrate, rhodium acetylacetonate, etc., and preferably rhodium chloride;

[0018] The loading method is commonly used in the art, including but not limited to urea deposition precipitation method, impregnation method, sol-gel method, etc., and preferably the urea deposition precipitation method;

[0019] The titanium-containing support is a titanium-containing material commonly used in the art, including but not limited to TiO2, uncalcined titanium silicalite TS-1-B with micropores blocked by a template agent, uncalcined titanium silicalite TS-2-B composed of nanoparticle accumulation, and the support is preferably uncalcined titanium silicalite TS-1-B with micropores blocked by a template agent.

[0020] The present invention is further configured such that in step (2):

[0021] The atmosphere for the high-temperature heat treatment is selected from one or more of hydrogen, oxygen, propylene, nitrogen, carbon monoxide, argon, and air, and preferably a hydrogen atmosphere;

[0022] The present invention is further configured such that in step (2):

[0023] The temperature of the high-temperature heat treatment is 200 - 400 °C, preferably 250 - 350 °C; the heating rate is 0.1 - 5 °C / minute, and the heat treatment time is 1 - 24 hours.

[0024] The third aspect of the present invention lies in providing the application of the above gold-rhodium heterostructure catalyst in the selective oxidation reaction of hydrocarbons.

[0025] The present invention is further configured such that the selective oxidation reaction of hydrocarbons includes but not limited to propylene epoxidation reaction and propane oxidation reaction.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] (1) Different from the bimetallic catalysts prepared by alloying or simple physical mixing in the prior art, the present invention constructs a catalyst with a metastable "hamburger"-type Au-Rh heterostructure by introducing rhodium atoms at the interface between gold atoms and the support, and effectively regulates the electronic state of gold through the interfacial electron fence structure, which can transform Au from the Au m+ state to the Au n- state, effectively activates molecular oxygen, and significantly improves the activity of the hydrocarbon selective oxidation reaction.

[0028] (2) The Au-Rh heterostructure catalyst developed by the present invention effectively inhibits the direct contact between rhodium and the reactants, avoids the occurrence of side reactions such as over-hydrogenation or over-oxidation, and ensures the selectivity of the target product.

[0029] (3) The Au-Rh heterostructure catalyst developed by the present invention has good stability, and the activity decreases by no more than 8% after 40 h of catalytic reaction.

[0030] (4) The preparation process of the catalyst developed by the present invention is simple, the controllability of the catalyst structure is strong, the metal utilization rate can be effectively improved, and the catalyst development cost can be reduced, which is of great significance for developing high-performance and high-stability catalysts required by industry. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1a-1f is the HAADF-STEM image of the Au-Rh 0.1 / TS-1-B catalyst prepared in Example 2 and the EDS mapping images of Au and Rh elements; wherein:

[0032] Figure 1a is the HAADF-STEM image of this catalyst; Figure 1b is an enlarged view of Figure 1a; Figure 1c is the Au element distribution map; Figure 1d is the Rh element distribution map; Figure 1e is the superposition map of Au and Rh element distributions; Figure 1f is the element line scan intensity distribution map along the selected position in Figure 1e.

[0033] Figure 2a-2e is the HAADF-STEM image of the Au-Rh 0.1 / TS-1-B catalyst prepared in Comparative Example 1 and the EDS mapping images of Au and Rh elements; wherein:

[0034] Figure 2a is the HAADF-STEM image of this catalyst; Figures 2b and 2c are enlarged views of Figure 2a; Figure 2d is the superposition map of Au and Rh element distributions; Figure 2e is the element line scan intensity distribution map along the selected position in Figure 2d.

[0035] Figure 3a-3d is for Au-Rh prepared in Comparative Example 4 0.3HAADF-STEM images of the / TS-1-B catalyst and EDS maps of Au and Rh elements; wherein:

[0036] Figure 3a is the HAADF-STEM image of the catalyst; Figure 3b is the superimposed map of the Au and Rh element distributions; Figures 3c and 3d are enlarged views of Figure 3a.

[0037] Figure 4a-4d For Comparative Example 6, the prepared Au-Rh 0.5 HAADF-STEM images of the / TS-1-B catalyst and EDS maps of Au and Rh elements; wherein:

[0038] Figure 4a is the HAADF-STEM image of a certain part of the catalyst; Figure 4b is an enlarged view of Figure 4a; Figure 4c is the HAADF-STEM image of another part of the catalyst; Figure 4d is an enlarged view of Figure 4c.

[0039] Figure 5a-5c Are the in-situ FTIR spectra of CO desorption on the catalysts prepared in Comparative Examples 2-3 and Example 2 respectively.

[0040] Figure 6a-6b Are the in-situ FTIR spectra of CO desorption on the catalysts prepared in Comparative Example 4 and Comparative Example 6 respectively.

[0041] Figure 7 Are the XPS analysis results of the catalysts prepared in Examples 1-3, Comparative Examples 2, 4-6.

[0042] Figure 8 Are the XANES spectra of the catalysts prepared in Example 2 and Comparative Example 2.

[0043] Figure 9a-9b Are the propylene conversion - activity volcano curve graph and propane conversion - activity volcano curve graph respectively.

[0044] Figure 10 Is the graph of the change of propylene epoxidation rate with time under the action of the catalyst prepared in Example 2. Detailed implementation manners

[0045] The technical solutions of the present invention will be further described in detail below through specific examples in combination with the accompanying drawings. However, these examples are only used to illustrate the present invention and do not limit the scope of the present invention. All other examples obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts fall within the protection scope of the present invention.

[0046] The materials used in the following examples are all conventional commercially available products. The experimental methods without specific conditions noted in the following examples are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer.

[0047] Glossary:

[0048] "Hamburger" type: The "hamburger" structure is a special metastable heterostructure. Taking the Au-Rh 0.1 / TS-1-B catalyst as an example, at the metal-support interface, the rhodium atomic layer is sandwiched between the gold nanoparticles and the support (TS-1-B zeolite), similar to the design of the middle layer in a hamburger.

[0049] The formation of this structure is achieved by precisely regulating the reduction kinetics of gold and rhodium. At the nanoscale, due to the guidance of stress and interaction, rhodium atoms preferentially migrate to the metal-support interface, while gold atoms tend to the outer shell layer. This structure significantly improves the interface stability, while avoiding intermetallic phase separation or other adverse reconstructions (such as ball-cup type or Janus type), and maintains excellent catalytic performance.

[0050] Electronic fence: In the present invention, the electronic fence is a region of electronic confinement effect formed by interfacial rhodium atoms. Specifically, in the catalyst with a "hamburger" type heterostructure, rhodium atoms are located between the gold atoms and the support interface, generating a unique electronic regulation effect, restricting the outward loss of electrons, and changing the valence state of gold atoms from the conventional positive valence (Au m+ ) to negative valence (Au n- ). This reversal of the electronic state significantly enhances the adsorption and activation ability of gold to molecular oxygen, while reducing the probability of side reactions (such as over-hydrogenation or peroxidation), thereby improving the activity and selectivity of the hydrocarbon selective oxidation reaction.

[0051] Core-shell heterostructure: The core-shell heterostructure refers to a structure with a "core-shell" hierarchical distribution inside the nanoparticles. Taking the Au-Rh heterostructure catalyst as an example, its core-shell structure shows that rhodium atoms are concentrated in the core region, while gold atoms are distributed in the outer shell layer. In the "hamburger" structure, the core-shell heterostructure further combines the electronic regulation effect of interfacial rhodium atoms, providing a highly stable geometric structure and adjustable electronic properties for the Au-Rh nanoparticles, thus maintaining the high efficiency and stability of the active sites in the catalytic reaction.

[0052] Example 1. Au-Rh 0.05 / TS-1-B catalyst

[0053] (1) Add 1 g of uncalcined titanium silicate molecular sieve TS-1-B with micropores blocked by the template agent and 39 mL of water into a beaker in sequence, mix and stir to obtain a suspension, and add 0.092 g of urea and a mixed precursor solution to the above suspension: 0.1 mL of chloroauric acid solution (0.956 mg Au / mL) and 6.5 μL of rhodium chloride solution (0.384 mg Rh(in mL), where the molar ratio of Au to Rh is 10:0.5.

[0054] (2) Heat the suspension in step (1) to 90 °C in a water bath and maintain for 6 h; separate the solid and liquid by centrifugation and wash. The obtained solid is vacuum dried at room temperature to obtain the loaded sample.

[0055] (3) In a hydrogen atmosphere, reduce the sample in step (2) at 310 °C for 1.5 h under an H2 / N2 atmosphere (H2 concentration is 40%) with a heating rate of 0.6 °C / min to obtain the Au-Rh 0.05 / TS-1-B catalyst. The HAADF-STEM image of this catalyst and the EDS mapping images of Au and Rh elements are as Figure 1a-1f shown. The average particle size of the gold nanoparticles in this catalyst is 2.6 nm.

[0056] Example 2, Au-Rh 0.1 / TS-1-B catalyst

[0057] The preparation method of the catalyst in this example is basically the same as that in Example 1, except that the amount of rhodium chloride solution (0.384 mg Rh / mL) is 13.0 μL, and the molar ratio of Au to Rh in the mixed precursor solution is 10:1, obtaining the Au-Rh 0.1 / TS-1-B catalyst. The average particle size of the gold nanoparticles in this catalyst is 2.7 nm.

[0058] Example 3, Au-Rh 0.15 / TS-1-B catalyst

[0059] The preparation method of the catalyst in this example is basically the same as that in Example 1, except that the amount of rhodium chloride solution (0.384 mg Rh / mL) is 19.5 μL, and the molar ratio of Au to Rh in the mixed precursor solution is 10:1.5, obtaining the Au-Rh 0.15 / TS-1-B catalyst. The average particle size of the gold nanoparticles in this catalyst is 2.5 nm.

[0060] Example 4, Au-Rh 0.01 / TS-1-B catalyst

[0061] The preparation method of the catalyst in this example is basically the same as that in Example 1, except that the amount of rhodium chloride solution (0.384 mg Rh / mL) is 1.3 μL, and the molar ratio of Au to Rh in the mixed precursor solution is 10:0.1, obtaining the Au-Rh 0.01 / TS-1-B catalyst, in which the average particle size of gold nanoparticles is 2.9 nm.

[0062] Example 5, Au-Rh 0.25 / TS-1-B catalyst

[0063] The preparation method of the catalyst in this example is basically the same as that in Example 1, except that the amount of rhodium chloride solution (0.384 mg Rh / mL) is 32.5 μL, and the molar ratio of Au to Rh in the mixed precursor solution is 10:2.5, obtaining the Au-Rh 0.01 / TS-1-B catalyst, in which the average particle size of gold nanoparticles is 2.5 nm.

[0064] Example 6, Au-Rh 0.1 / TS-2-B catalyst

[0065] The preparation method of the catalyst in this example is basically the same as that in Example 2, except that the support is the uncalcined titanium silicalite TS-2-B composed of stacked nanoparticles, obtaining the Au-Rh 0.1 / TS-2-B catalyst.

[0066] Example 7, Au-Rh 0.1 / TiO2 catalyst

[0067] The preparation method of the catalyst in this example is basically the same as that in Example 2, except that the support is TiO2, obtaining the Au-Rh 0.1 / TiO2 catalyst.

[0068] Example 8, Preparation of Au-Rh by incipient wetness impregnation method 0.1 / TS-1-B catalyst

[0069] (1) Take 1 g of uncalcined titanium silicalite TS-1-B with micropores blocked by the template agent and place it in a 25 mL polytetrafluoroethylene crucible. Then, dropwise add 1 mL of sodium thioaurate aqueous solution (0.956 mg Au / mL) and 13.0 μL of rhodium chloride solution (0.384 mg Rh / mL), and continuously stir with a glass rod during the dropping process.

[0070] (2) After the dropping is completed, let it stand at room temperature and in the dark for about 12 h. Finally, place the polytetrafluoroethylene crucible in a vacuum desiccator and evacuate it for about 12 h to obtain the Au-Rh 0.1 / TS-1-B catalyst.

[0071] Example 9, Au-Rh 0.1 / TS-1-B catalyst

[0072] In this example, the preparation method of the catalyst is basically the same as that in Example 2, except that the reduction temperature is 250 °C, and Au-Rh 0.1 / TS-1-B catalyst is obtained.

[0073] Example 10, Au-Rh 0.1 / TS-1-B catalyst

[0074] In this example, the preparation method of the catalyst is basically the same as that in Example 2, except that the reduction temperature is 350 °C, and Au-Rh 0.1 / TS-1-B catalyst is obtained.

[0075] Comparative Example 1, Au-Rh 0.1 / TS-1-B catalyst

[0076] In this comparative example, the preparation method of the catalyst is basically the same as that in Example 2, except that the reduction temperature is 810 °C, and Au-Rh 0.1 / TS-1-B catalyst is obtained. The HAADF-STEM image of this catalyst and the EDS mapping images of Au and Rh elements are as Figure 2a-2e shown.

[0077] Comparative Example 2, Au / TS-1-B catalyst

[0078] In this example, the preparation method of the catalyst is basically the same as that in Example 2, except that only chloroauric acid is used as the precursor. In step (1), 0.092 g of urea and 0.1 mL of chloroauric acid solution (0.956 mg Au / mL) are added to the suspension to obtain Au / TS-1-B catalyst.

[0079] Comparative Example 3, Rh / TS-1-B catalyst

[0080] In this comparative example, the preparation method of the catalyst is basically the same as that in Example 2, except that only rhodium chloride is used as the precursor. In step (1), 0.092 g of urea and 13.0 μL of rhodium chloride solution (0.384 mg Rh / mL) are added to the suspension to obtain Rh / TS-1-B catalyst.

[0081] Comparative Example 4, Au-Rh 0.3 / TS-1-B catalyst

[0082] In this comparative example, the preparation method of the catalyst is basically the same as that in Example 2, except that the amount of rhodium chloride solution (0.384 mg Rh / mL) is 39.0 μL, and the molar ratio of Au to Rh in the mixed precursor solution is 10:3, and Au-Rh is obtained0.3 / TS-1-B catalyst. The HAADF-STEM image of this catalyst and the EDS mapping images of Au and Rh elements are as Figure 3a-3d shown.

[0083] Comparative Example 5, Au-Rh 0.4 / TS-1-B catalyst

[0084] The preparation method of the catalyst in this comparative example is basically the same as that of Example 2, except that the amount of rhodium chloride solution (0.384 mg Rh / mL) is 52.0 μL. In the mixed precursor solution, the molar ratio of Au to Rh is 10:4, and an Au-Rh 0.4 / TS-1-B catalyst is obtained.

[0085] Comparative Example 6, Au-Rh 0.5 / TS-1-B catalyst

[0086] The preparation method of the catalyst in this comparative example is basically the same as that of Example 2, except that the amount of rhodium chloride solution (0.384 mg Rh / mL) is 65.0 μL. In the mixed precursor solution, the molar ratio of Au to Rh is 10:5, and an Au-Rh 0.5 / TS-1-B catalyst is obtained. The HAADF-STEM image of this catalyst and the EDS mapping images of Au and Rh elements are as Figure 4a-4d shown.

[0087] Catalyst performance test

[0088] The catalysts prepared in the above Examples 1-10 and Comparative Examples 1-6 were evaluated for catalytic performance in the reactions of gas-phase epoxidation of propylene to prepare propylene oxide (PO) and oxidation of propane to prepare acetone (ACE). The reaction was carried out in a fixed-bed reactor at atmospheric pressure. The reaction atmosphere composition was propylene (propane): hydrogen: oxygen: nitrogen = 1:1:1:7 (volume ratio), and the space velocity was 4000 - 14000 mL·h -1 ·g cat -1 . The reaction temperature was 200 °C, and the outlet products were analyzed by gas chromatography. The catalytic results are shown in Tables 1 and 2 below.

[0089] The in-situ FTIR spectra of CO desorption on the catalysts prepared in Comparative Examples 2-3 and Example 2 are as Figure 5a-5c shown.

[0090] The in-situ FTIR spectra of CO desorption on the catalysts prepared in Comparative Example 4 and Comparative Example 6 are as Figure 6a-6b shown.

[0091] The XPS analysis results of the catalysts prepared in Examples 1-3, Comparative Example 2, and Comparative Examples 4-6 are as follows Figure 7 shown

[0092] The XANES spectra of the catalysts prepared in Example 2 and Comparative Example 2 are as follows Figure 8 shown

[0093] The propylene conversion - activity volcano curve and propane conversion - activity volcano curve diagrams are as follows Figure 9a-9b shown

[0094] The diagram showing the change of propylene epoxidation rate with time under the action of the catalyst prepared in Example 2 is as follows Figure 10 shown

[0095] Table 1 Catalytic results of different catalysts in the gas-phase epoxidation of propylene

[0096]

[0097]

[0098] Table 2 Catalytic results of different catalysts in the oxidation of propane

[0099]

[0100] Figure 1a-1f The HAADF-STEM and EDS mapping diagrams of the catalyst prepared in Example 2 as shown confirm that the bimetallic nanoparticles form a Rh-Au core-shell heterostructure, and the Rh atomic layer is preferentially enriched at the Au-TS-1-B interface Figure 2a-2e It shows that when the reduction temperature is increased from 310 °C to 810 °C, phase separation occurs in the Au-Rh particles, forming isolated Au and Rh nanoparticles. This indicates that lower-temperature reduction is a key parameter for inducing the metastable "hamburger"-type heterostructure

[0101] Comparing the data of Example 2, Examples 9-10, and Comparative Example 1 in Tables 1-2 above, it can be seen that the performance of the catalysts prepared at lower reduction temperatures (250-350 °C) is significantly better than that of the catalysts reduced at a high temperature of 810 °C. Therefore, during the catalyst preparation process, the thermal reduction temperature is preferably 250-350 °C

[0102] Figure 3a-3d (Comparative Example 4) and Figure 4a-4d (Comparative Example 6) show that as the Rh content increases, the Au-Rh structure changes from "ball-cup-shaped" (Au / Rh molar ratio of 10:3) to "Janus-type" (Au / Rh molar ratio of 10:6), and EDS mapping and lattice fringe analysis show that the Rh element is gradually exposed on the surface. Combining Figure 5a-5c and Figure 6a-6bIn-situ FTIR spectroscopy revealed that when Rh was completely encapsulated by Au (Example 2), the CO adsorption peak only appeared at 2075 - 2040 cm -1 (Au 0 -CO); while when Rh was exposed (Comparative Example 6), the peak intensity of 2030 - 2000 cm -1 (Rh 0 -CO) increased significantly, demonstrating that the degree of interfacial embedding and exposure of Rh could be precisely regulated by the Rh loading amount.

[0103] Combined with the data in Table 1 - 2 above, when there was an excess of Rh, the Au - Rh structure changed from complete encapsulation to "cup - and - ball" and "Janus - type", resulting in over - hydrogenation or over - oxidation reactions, and a significant decrease in the product formation rate and selectivity. Thus, it was shown that the core of performance optimization was that Rh was embedded at the interface between Au and the support without being exposed in the interfacial electron - fence effect region, thereby avoiding contact with reactants. Therefore, the Au / Rh molar ratio was preferably 10:(0.1 - 2.5).

[0104] Figure 7 XPS analysis showed that: as the Rh content increased, the Au 4f binding energy decreased from 84.2 eV (Au / TS - 1 - B) to 83.6 eV (Au - Rh 0.5 / TS - 1 - B), and the Au electron density increased. Figure 8 The XANES spectrum showed that Au existed in the Au m+ state in pure Au / TS - 1 - B, while in Au - Rh 0.1 / TS - 1 - B it changed to the Au n- state, confirming that the embedding of Rh induced interfacial charge transfer.

[0105] From Table 1 - 2 above and Figure 9a-9b the propylene conversion - activity volcano curve, propane conversion - activity volcano curve, it could be obtained that:

[0106] When the Au / Rh molar ratio was 10:1 (i.e., when Rh was completely embedded at the Au - TS - 1 - B interface), the production rate of propylene oxide could be as high as 502.57 g PO ·kg cat -1 ·h -1 , which was nearly three times higher than that of the traditional Au / TS - 1 - B catalyst (180.19 g PO ·kg cat -1 ·h -1 ); the production rate of acetone could reach 184.56 g ACE ·kg cat -1 ·h -1, nearly twice that of the Au / TS-1-B catalyst; at the same time, the selectivities of propylene oxide and acetone can reach 61.79% and 75.51% respectively, overcoming the activity-selectivity contradiction problem existing in the existing catalysts in the selective oxidation reaction.

[0107] In addition, combined with Figure 10 As can be seen from the change of the epoxidation rate with time shown in, the catalyst prepared by the present invention also has good stability. After reacting for 40 h, the activity decrease does not exceed 8%.

[0108] This application has been described in detail, aiming to enable those skilled in the art to understand the content of this application and implement it. However, it cannot be used to limit the protection scope of this application. Any equivalent changes or modifications made according to the spirit and essence of this application should be covered within the protection scope of this application.

Claims

1. A gold-rhodium heterostructure catalyst, characterized in that, The catalyst has a "hamburger" structure, including a support and metal particles supported on the support. The metal particles have a metastable gold-rhodium core-shell heterostructure, wherein the gold nanoparticles form the outer shell layer of the metal particles, and rhodium atoms are embedded at the interface between the gold nanoparticles and the support to form an electron fence.

2. The gold-rhodium heterostructure catalyst according to claim 1, characterized in that, The average particle size of the gold nanoparticles is less than 10 nm, preferably 1-5 nm.

3. The Au-Rh heterostructure catalyst according to claim 1, wherein The support is a titanium-containing material, selected from one or more of TiO2, uncalcined titanium silicalite TS-1-B with micropores blocked by a templating agent, and uncalcined titanium silicalite TS-2-B composed of stacked nanoparticles, preferably uncalcined titanium silicalite TS-1-B with micropores blocked by a templating agent.

4. The preparation method of the gold-rhodium heterostructure catalyst according to any one of claims 1-3, characterized in that, The method comprises the following steps: (1) Loading a gold precursor solution and a rhodium precursor solution onto the titanium-containing support; (2) Performing high-temperature heat treatment under a certain atmosphere.

5. The preparation method of the gold-rhodium heterostructure catalyst according to claim 4, wherein, In the step (1): The feeding amounts of the gold precursor solution and the rhodium precursor solution are set according to the gold-rhodium molar ratio, and the gold-rhodium molar ratio is 10:(0.1-2.5), preferably 10:(0.5-1.5).

6. The preparation method of the gold-rhodium heterostructure catalyst according to claim 4, characterized in that, In the step (1): The gold precursor is selected from one or more of chloroauric acid, sodium thiosulfogoldate, and gold hydroxide; preferably chloroauric acid; The rhodium precursor is selected from one or more of rhodium chloride, rhodium nitrate, and rhodium acetylacetonate, preferably rhodium chloride; The loading method is selected from one of urea deposition precipitation method, impregnation method, and sol-gel method, preferably urea deposition precipitation method; The titanium-containing support is selected from one or more of TiO2, uncalcined titanium silicalite TS-1-B with micropores blocked by a templating agent, and uncalcined titanium silicalite TS-2-B composed of stacked nanoparticles, and the support is preferably uncalcined titanium silicalite TS-1-B with micropores blocked by a templating agent.

7. The preparation method of the gold-rhodium heterostructure catalyst according to claim 4, characterized in that, In the step (2): The atmosphere for the high-temperature heat treatment is selected from one or more of hydrogen, oxygen, propylene, nitrogen, carbon monoxide, argon, and air, preferably a hydrogen atmosphere.

8. The preparation method of the gold-rhodium heterostructure catalyst according to claim 4, characterized in that, In the step (2): The temperature of the high-temperature heat treatment is 200-400 °C, preferably 250-350 °C; the heating rate is 0.1-5 °C / minute, and the heat treatment time is 1-24 hours.

9. Application of a gold-rhodium heterostructure catalyst, characterized in that, The catalyst is the gold-rhodium heterostructure catalyst according to any one of claims 1-3, and is used for the selective oxidation reaction of hydrocarbons.

10. Use of the gold-rhodium heterostructure catalyst according to claim 9, characterized in that, The selective oxidation reaction of hydrocarbons includes propylene epoxidation reaction and propane oxidation reaction.

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