Low-loading reverse spinel structure solid catalyst and method for preparing the same
By constructing a catalyst with a low-loaded reverse spinel structure on a molecular sieve support, the problems of insufficient activity and reduced accessibility of supported heterogeneous catalysts were solved, and the synergistic optimization of the properties and spatial distribution of active sites was achieved, thereby improving the catalytic reaction efficiency.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- QINGDAO UNIV OF SCI & TECH
- Filing Date
- 2026-03-26
- Publication Date
- 2026-06-19
Smart Images
Figure CN122230787A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of solid catalytic materials, specifically to a low-loaded Lewis acid solid catalyst based on the antiphase spinel structure and its preparation method, belonging to the field of heterogeneous catalytic materials technology, and can be used in catalytic reaction systems involving macromolecular substrates. Background Technology
[0002] Polyethylene terephthalate (PET) is a widely used polyester material, widely used in packaging, textiles, and engineering materials due to its excellent mechanical and processing properties. With the continuous growth of PET production, the resource recycling of waste PET has become increasingly prominent. Chemical depolymerization, as an important pathway to achieve a closed-loop polyester cycle, can convert PET into low-molecular-weight monomers or intermediates. Among these, ethylene glycol alcoholysis, due to its mild reaction conditions and the direct repolymerization of the product, diethyl terephthalate (BHET), has become one of the important technical routes for polyester chemical recycling.
[0003] In the chemical depolymerization of polyester, the catalyst has a decisive influence on the reaction efficiency and product selectivity. Existing catalytic systems mainly include two categories: homogeneous catalysts and heterogeneous catalysts. Homogeneous catalysts have high catalytic activity, but they suffer from problems such as difficult separation, low recycling efficiency, and environmental risks. In contrast, heterogeneous catalysts have advantages such as easy separation and recyclability, and have become a key research direction in polyester depolymerization.
[0004] Among heterogeneous catalysts, supported heterogeneous catalysts have been widely used in polyester depolymerization reactions due to their high specific surface area and tunable distribution of active sites. However, existing supported heterogeneous catalysts still have certain limitations in practical applications. Since polyester is a macromolecular substrate, its depolymerization reaction is usually limited by the spatial accessibility of active sites, and the reaction mainly occurs on the outer surface or pore region of the catalyst. In this case, the catalytic performance of the catalyst depends not only on the number of active sites, but also on their spatial distribution and accessibility.
[0005] To improve catalytic activity, current research typically increases the number of Lewis acid sites by increasing the loading of metal oxides. However, under high loading conditions, active components easily enter or clog the support pores, reducing the diffusion efficiency of reactants and intermediates, thus weakening the accessibility of active sites. While under low loading conditions, although pore clogging can be avoided, the number of active sites is limited, and the catalytic performance is insufficient to meet the reaction requirements. Therefore, existing catalytic systems generally suffer from a performance contradiction of "insufficient activity at low loading and decreased accessibility at high loading," making it difficult to achieve an effective balance between catalytic activity and active site accessibility.
[0006] Furthermore, existing research largely focuses on optimizing catalytic performance by adjusting metal loading or dispersion, while lacking effective strategies for controlling the internal structure of the active phase, particularly the cation coordination environment and its influence on Lewis acid properties. How to achieve synergistic optimization of active site properties and spatial accessibility through structural modulation under low loading conditions remains a pressing technical challenge in this field. Summary of the Invention
[0007] To overcome the above-mentioned technical problems, the present invention provides a low-loaded reverse spinel solid catalyst and its preparation method.
[0008] To achieve the above objectives, the present invention adopts the following technical solution:
[0009] I. A low-loaded reversed-phase spinel solid catalyst, wherein the catalyst uses a molecular sieve as a support, the molecular sieve has a framework silicon-to-aluminum ratio greater than 25, the active component of the catalyst is a spinel structure oxide of type MAl2O4 with a partially reversed-phase structure, and the loading of the active component is 0.1 wt% to 1.5 wt%.
[0010] Furthermore, in the MAl2O4 type spinel structure oxide, M is selected from one of Zn, Mg or Co.
[0011] Furthermore, the partially inverted structure is a partial exchange of metal cations between four-coordinate sites and six-coordinate sites in the spinel lattice.
[0012] Furthermore, the inverted structure accounts for 10% to 45%.
[0013] II. The preparation method of the above-mentioned low-loaded reverse-phase spinel solid catalyst includes the following steps:
[0014] S1. Dissolve the metal salt and aluminum nitrate in deionized water to prepare a precursor solution;
[0015] S2. The precursor solution is loaded onto a molecular sieve support by an impregnation method, and dried to obtain a molecular sieve support loaded with the precursor.
[0016] S3. The molecular sieve support for the supported precursor is calcined at 450–600 °C to obtain the catalyst.
[0017] Furthermore, the metal salt mentioned in step S1 is a metal nitrate.
[0018] Furthermore, the roasting time in step S3 is 1 to 4 hours.
[0019] The technical principles and beneficial effects of this invention are as follows:
[0020] This invention achieves synergistic optimization of the properties and spatial distribution of active sites by constructing a spinel active phase with a partially inverted structure under low-load conditions.
[0021] Compared with the prior art, the present invention can maintain high catalytic performance under low load conditions, while avoiding the problem of active components entering or clogging the pores of the support under high load conditions.
[0022] Furthermore, the catalyst of the present invention is particularly suitable for catalytic reaction systems involving macromolecular substrates, as it provides catalytic active sites while facilitating contact between reactants and active sites. Attached Figure Description
[0023] To more clearly illustrate the specific embodiments of the present invention, the accompanying drawings used in the specific embodiments will be briefly described below:
[0024] Figure 1 This is a flowchart of a method for preparing a low-loaded reversed spinel solid catalyst according to the present invention.
[0025] Figure 2 Zn 2p of the catalyst prepared in Example 1 of this invention 3 / 2 XPS spectrum;
[0026] Figure 3 This is a comparison of the N2 adsorption-desorption isotherms of the catalyst prepared in Example 1 of this invention and the molecular sieve support;
[0027] Figure 4 Zn 2p of the catalyst prepared in Comparative Example 1 of this invention 3 / 2 XPS spectrum;
[0028] Figure 5 This is a comparison diagram of the NH3-TPD of the catalyst prepared in Comparative Example 1 and the catalyst prepared in Example 1 of the present invention.
[0029] Figure 6 Zn 2p of the catalyst prepared in Comparative Example 2 of this invention 3 / 2 XPS spectrum;
[0030] Figure 7 This is a comparison diagram of the N2 adsorption-desorption isotherms of the catalyst prepared in Comparative Example 2 of the present invention and the molecular sieve support.
[0031] Figure 8 Zn 2p of the catalyst prepared in Comparative Example 3 of this invention 3 / 2 XPS spectrum;
[0032] Figure 9 This is a comparison diagram of the N2 adsorption-desorption isotherms of the catalyst prepared in Comparative Example 3 of the present invention and the molecular sieve support. Detailed Implementation
[0033] To make the objectives, technical solutions, and beneficial effects of this invention clearer, the invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are for illustrative purposes only and are not intended to limit the scope of protection of this invention. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.
[0034] Figure 1 This diagram illustrates a flow chart of a method for preparing a low-loaded reversed-phase spinel solid catalyst according to the present invention. The catalyst prepared by this method constructs low-loaded reversed-phase spinel active sites on a molecular sieve support. While maintaining the integrity of the support's pore structure, this reduces the occupation of pores by the active components, thereby improving the accessibility of the active sites. Simultaneously, the formation of the reversed-phase structure helps enhance the acidity of the catalyst. Based on these structural features, the catalyst of the present invention is more conducive to the effective contact between macromolecular substrates and active sites, and improves catalytic reaction efficiency.
[0035] The method for characterizing the degree of phase inversion in this invention is as follows: X-ray photoelectron spectroscopy (XPS) is used to test the characteristic peaks of metal elements, wherein metal species under different coordination environments correspond to characteristic peaks with different binding energies, and peak fitting is performed on them. The relative content of the corresponding coordination structure is calculated based on the peak area ratio of each peak, thereby obtaining the proportion of the phase inversion structure, i.e., the degree of phase inversion.
[0036] Example 1
[0037] S1. Weigh approximately 0.12 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and approximately 0.31 g of aluminum nitrate nonahydrate (Al(NO3)3·9H2O), dissolve them in approximately 2.5 mL of deionized water, and stir until completely dissolved to obtain the precursor solution;
[0038] S2. The above precursor solution was loaded onto about 5 g of ZSM-5 molecular sieve support (skeletal silica-alumina ratio of 50) using an equal-volume impregnation method. After impregnation, the sample was placed in an 80 ℃ oven and dried for about 12 h to obtain the molecular sieve support loaded with the precursor.
[0039] S3. The molecular sieve support for the supported precursor is placed in a muffle furnace and calcined at 500 °C for 3 h to obtain the low-loaded reverse spinel solid catalyst, wherein the active component is ZnAl2O4 and its loading is about 1.5 wt%.
[0040] Figure 2 The Zn 2p of the catalyst prepared in Example 1 is shown. 3 / 2XPS spectra show different peaks corresponding to Zn species under different coordination environments. The degree of phase inversion is calculated to be approximately 26.8% based on the peak fitting results, indicating the formation of a partially inverted spinel structure.
[0041] Figure 3 The diagram shows a comparison of the N2 adsorption-desorption isotherms of the catalyst prepared in Example 1 and the molecular sieve support. The catalyst still maintains a high specific surface area, indicating that no obvious pore blockage phenomenon has occurred.
[0042] Example 2
[0043] S1. Weigh approximately 0.045 g of magnesium nitrate hexahydrate (Mg(NO3)2·6H2O) and approximately 0.13 g of aluminum nitrate nonahydrate (Al(NO3)3·9H2O), dissolve them in approximately 2.5 mL of deionized water, and stir until completely dissolved to obtain the precursor solution;
[0044] S2. The above precursor solution was loaded onto about 5 g of silicalite-1 molecular sieve support (all-silica molecular sieve, without aluminum framework) using an equal-volume impregnation method. After impregnation, the sample was placed in an 80 ℃ oven and dried for about 12 h to obtain the molecular sieve support loaded with the precursor.
[0045] S3. The molecular sieve support for the supported precursor is placed in a muffle furnace and calcined at 600 °C for 4 h to obtain the low-loaded reverse spinel solid catalyst. The active component in the obtained catalyst is MgAl2O4, and its loading is about 0.5 wt%.
[0046] The obtained catalyst was subjected to X-ray photoelectron spectroscopy (XPS) and peak fitting analysis was performed on the characteristic peaks related to Mg. The results showed that the peak area ratio of Mg species in the catalyst under different coordination environments corresponded to an inversion degree of approximately 15.7%, indicating the formation of a partially inverted spinel structure.
[0047] The obtained catalyst was subjected to N2 adsorption-desorption tests, and the results showed that the catalyst still maintained a high specific surface area and no obvious pore blockage phenomenon was observed.
[0048] Comparative Example 1
[0049] S1. Weigh approximately 0.12 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and approximately 0.31 g of aluminum nitrate nonahydrate (Al(NO3)3·9H2O), dissolve them in approximately 2.5 mL of deionized water, and stir until completely dissolved to obtain the precursor solution;
[0050] S2. The above precursor solution was loaded onto about 5 g of ZSM-5 molecular sieve support (skeletal silica-alumina ratio of 50) using an equal-volume impregnation method. After impregnation, the sample was placed in an 80 ℃ oven and dried for about 12 h to obtain the molecular sieve support loaded with the precursor.
[0051] S3. The molecular sieve support for the supported precursor is placed in a muffle furnace and calcined at 400 °C for 3 h to obtain the low-loaded solid catalyst, wherein the active component is ZnAl2O4 and its loading is about 1.5 wt%.
[0052] Figure 4 The Zn 2p of the catalyst prepared in Comparative Example 1 is shown. 3 / 2 The XPS spectrum shows that, compared with Example 1, under the same loading and support conditions, no obvious reverse-phase structure characteristic peaks were observed in this catalyst due to the lower calcination temperature.
[0053] Figure 5 The NH3-TPD comparison diagrams of the catalyst prepared in Comparative Example 1 and the catalyst prepared in Example 1 are shown. Compared with Comparative Example 1, which does not have a reversed structure, Example 1 shows higher desorption peak intensities in the medium-strong acid and strong acid regions, indicating that the formation of the reversed structure helps to regulate the acid properties of the catalyst.
[0054] Comparative Example 2
[0055] S1. Weigh approximately 0.40 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and approximately 1.03 g of aluminum nitrate nonahydrate (Al(NO3)3·9H2O), dissolve them in approximately 2.5 mL of deionized water, and stir until completely dissolved to obtain the precursor solution;
[0056] S2. The above precursor solution was loaded onto about 5 g of ZSM-5 molecular sieve support (skeletal silica-alumina ratio of 50) using an equal-volume impregnation method. After impregnation, the sample was placed in an 80 ℃ oven and dried for about 12 h to obtain the molecular sieve support loaded with the precursor.
[0057] S3. The molecular sieve support for the precursor is placed in a muffle furnace and calcined at 500 °C for 3 h to obtain the solid catalyst, wherein the active component is ZnAl2O4 and its loading is about 5.0 wt%.
[0058] Figure 6 The Zn 2p of the catalyst prepared in Comparative Example 2 is shown. 3 / 2 XPS spectra show different peaks corresponding to Zn species under different coordination environments. The degree of phase inversion is calculated to be approximately 22.5% based on the peak fitting results, indicating that a partially inverted spinel structure was still formed under these conditions.
[0059] Figure 7 The N2 adsorption-desorption isotherms of the catalyst prepared in Comparative Example 2 and the molecular sieve support are shown in the figure. The results show that the specific surface area of the catalyst is reduced compared with Example 1, indicating that under higher loading conditions, some pores may be occupied by active components, which will have a certain impact on the pore structure of the support.
[0060] Comparative Example 3
[0061] S1. Weigh approximately 0.12 g of zinc nitrate hexahydrate (Zn(NO3)2·6H2O) and approximately 0.31 g of aluminum nitrate nonahydrate (Al(NO3)3·9H2O), dissolve them in approximately 2.5 mL of deionized water, and stir until completely dissolved to obtain the precursor solution;
[0062] S2. The above precursor solution was loaded onto about 5 g of ZSM-5 molecular sieve support (skeletal silica-alumina ratio of 50) using an equal-volume impregnation method. After impregnation, the sample was placed in an 80 ℃ oven and dried for about 12 h to obtain the molecular sieve support loaded with the precursor.
[0063] S3. The molecular sieve support for the supported precursor is placed in a muffle furnace and calcined at 800 °C for 3 h to obtain the low-loaded solid catalyst, wherein the active component is ZnAl2O4 and its loading is about 1.5 wt%.
[0064] Figure 8 The Zn 2p of the catalyst prepared in Comparative Example 3 is shown. 3 / 2 XPS spectra, with different peaks corresponding to Zn species under different coordination environments. The phase inversion degree is calculated to be approximately 11.1% based on the peak fitting results.
[0065] Figure 9 The N2 adsorption-desorption isotherms of the catalyst prepared in Comparative Example 3 and the molecular sieve support are shown in the figure. The results show that, compared with Example 1, the adsorption characteristics related to micropores in the catalyst are significantly weakened and the specific surface area is significantly reduced. This indicates that under high-temperature calcination conditions, the molecular sieve framework structure is destroyed and the pore structure collapses.
[0066] The PET ethylene glycol alcoholysis performance of the catalysts prepared in the examples and comparative examples was tested under the following conditions:
[0067] A 250 mL four-necked flask was used as the reactor, and the reaction was carried out under a nitrogen atmosphere at a temperature of 196 °C. The catalyst dosage was 5% of the mass of PET, and the molar ratio of ethylene glycol to PET was 9:1. Under these conditions, the reaction time required for complete PET conversion was investigated, and the results are listed in Table 1.
[0068] Table 1. Comparison of the structural properties of different catalysts and their performance in the alcoholysis reaction of PET glycol.
[0069] According to the results in Table 1:
[0070] (1) Compared with Comparative Example 1, under the same reaction conditions, the catalyst prepared in Example 1 exhibited significantly higher catalytic activity in the alcoholysis reaction of PET ethylene glycol, and its complete conversion time was significantly shortened. This indicates that the formation of the reverse spinel structure helps to regulate the properties of the active sites, thereby improving the catalytic reaction efficiency.
[0071] (2) Compared with Comparative Example 2, under the same reversed-phase structure conditions, Example 1 maintained high catalytic activity at a lower loading, while the catalytic performance of the high-loading sample decreased significantly. This indicates that under similar reversed-phase structure conditions, the spatial accessibility of active sites has a key impact on catalytic performance. Excessive loading of active components will affect the pore structure of the support, reduce the accessibility of active sites, and thus hinder the reaction.
[0072] (3) Compared with Comparative Example 3, under the same reaction conditions, the catalyst prepared in Example 1 exhibited excellent catalytic performance while maintaining the integrity of the molecular sieve framework structure. Although a certain proportion of reversed-phase structure was still detected in Comparative Example 3, the accessibility of active sites was significantly reduced due to the collapse of the support pore structure, resulting in a decrease in catalytic performance. This indicates that a good pore structure plays an important role in the catalytic conversion of macromolecular substrates.
[0073] (4) In Example 2, good catalytic activity can still be achieved on a molecular sieve support without aluminum framework, indicating that the activity of the catalytic system mainly comes from the spinel active phase rather than the acidity of the molecular sieve framework, and the catalytic performance is not only related to the specific surface area, but also closely related to the properties and spatial distribution of the active sites.
[0074] In summary, this invention constructs a spinel active phase with a partially reversed structure under low loading conditions, thereby achieving synergistic optimization of the properties and spatial accessibility of active sites while ensuring the integrity of the support pore structure, thus significantly improving the catalytic conversion efficiency of polyester macromolecular substrates.
[0075] Please note that the technical features of the above embodiments can be combined arbitrarily. For the sake of brevity, not all possible combinations of the technical features in the above embodiments have been described. However, as long as the combination of these technical features does not contradict each other, it should be considered within the scope of this specification. The above embodiments only illustrate several implementation methods of this application, and their descriptions are relatively specific and detailed, but they should not be construed as limiting the scope of the invention patent.
Claims
1. A low-loading reversed spinel solid catalyst, characterized in that, The catalyst uses a molecular sieve as a support, the molecular sieve has a framework silicon-to-aluminum ratio greater than 25, the active component of the catalyst is a spinel structure oxide of MAl2O4 with a partially reversed structure, and the loading of the active component is 0.1 wt% to 1.5 wt%.
2. The low-loading reversed spinel solid catalyst according to claim 1, characterized in that, In the MAl2O4 type spinel structure oxide, M is selected from one of Zn, Mg or Co.
3. The low-loading reversed spinel solid catalyst according to claim 1, wherein, The partially reversed structure is formed by the partial exchange of metal cations between four-coordinate sites and six-coordinate sites in the spinel lattice.
4. The low-loading reversed spinel solid catalyst according to claim 1, wherein, The proportion of the antiphase structure is 10% to 45%.
5. A process for the preparation of a low-loaded reversed spinel solid catalyst according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Dissolve the metal salt and aluminum nitrate in deionized water to prepare a precursor solution; S2. The precursor solution is loaded onto a molecular sieve support by an impregnation method, and dried to obtain a molecular sieve support loaded with the precursor. S3. The molecular sieve support for the supported precursor is calcined at 450–600 °C to obtain the catalyst.
6. The method for preparing a low-loaded reversed spinel solid catalyst according to claim 5, characterized in that, The metal salt mentioned in step S1 is a metal nitrate.
7. A method for preparing a low-loaded reversed spinel solid catalyst according to claim 5, characterized in that, The roasting time in step S3 is 1 to 4 hours.