A monodisperse nanoscale BaO-supported MWW molecular sieve catalyst, its preparation method and application
By loading nanoscale BaO onto MWW molecular sieves, the problems of easy aggregation of BaO and poor accessibility of active sites were solved, achieving highly efficient catalysis of PET saccharification reaction. The catalyst has high activity and high stability, and the BHET yield reaches 98%.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- FUDAN UNIVERSITY
- Filing Date
- 2026-03-03
- Publication Date
- 2026-06-30
AI Technical Summary
Existing catalysts have poor BaO aggregation and accessibility of active sites, resulting in low efficiency of PET saccharification reaction and difficulty in achieving efficient chemical recycling.
Using MWW molecular sieve as a support, nanoscale BaO was loaded via solid-state metallization. The layered structure and surface hydroxyl groups of MWW molecular sieve were utilized to achieve high dispersion of BaO nanoparticles, thus preparing a monodisperse nanoscale BaO-supported MWW molecular sieve catalyst.
It significantly improves the PET saccharification efficiency, with BHET monomer yield reaching over 98%. The catalyst has high activity, high stability, and good recyclability, making it suitable for large-scale production.
Smart Images
Figure CN122298524A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of catalytic materials technology, specifically relating to a monodisperse nanoscale BaO-supported MWW molecular sieve catalyst, its preparation method, and its application. Background Technology
[0002] Polyethylene terephthalate (PET), as an important thermoplastic polymer, is widely used in packaging, textiles, and electronics due to its excellent mechanical properties, chemical stability, and processing performance. Market research predicts that the global PET market will reach US$36.6 billion by 2029, with a compound annual growth rate of approximately 6.29%, highlighting its significant industrial importance. However, the large-scale production and consumption of PET also brings serious environmental challenges. Currently, the global recycling rate of PET waste is less than 10%, and its inherent resistance to degradation leads to the accumulation of large amounts of waste in the natural environment, posing a potential threat to ecosystems and human health.
[0003] To address the issue of PET waste, existing treatment technologies mainly include three pathways: energy recovery, physical recovery, and chemical recovery. Among these, mechanical recovery, as the mainstream treatment method, is limited by the thermal and mechanical stability of PET materials. During repeated processing, molecular chains are prone to breakage, leading to significant deterioration of material properties and a "downgraded recycling" phenomenon, making it difficult to achieve high-value recycling. While heat recovery methods can achieve energy recovery, they may generate harmful gases during the process, posing a risk of secondary pollution, and are also less economically viable.
[0004] In contrast, chemical recycling, particularly ethylene glycol glycolysis, has garnered significant attention in recent years due to its ability to efficiently depolymerize PET into bis(2-hydroxyethyl) terephthalate (BHET) monomers, achieving a true closed-loop cycle. This technological approach offers advantages such as relatively mild reaction conditions, recyclable and environmentally friendly solvents, and high product purity, making it considered one of the most promising chemical recycling methods for PET for industrialization. More importantly, BHET monomers can be directly used to regenerate high-quality PET, effectively reducing dependence on fossil fuels and aligning with sustainable development requirements.
[0005] However, the kinetics of PET saccharification are slow and inefficient without a catalyst, making the development of high-performance catalysts crucial for the commercial application of this technology. Currently reported PET saccharification catalyst systems mainly include: ① Homogeneous catalysts, such as metal acetates and titanates, which, while exhibiting high activity, suffer from problems such as heavy metal toxicity, equipment corrosion, and difficulty in separation and recovery; ② Heterogeneous catalysts, including solid acids, metal oxides, and hydrotalcites, which, while recyclable, generally face challenges such as poor accessibility of active sites, limited specific surface area, and difficulty in balancing activity and stability; ③ Emerging catalytic materials, such as ionic liquids, enzyme catalysts, and nanomaterials, which, while showing good potential, still have limitations such as high cost, poor stability, or complex preparation.
[0006] Among numerous catalytic materials, alkaline earth metal oxides, especially BaO, exhibit good catalytic potential in transesterification reactions due to their moderate basicity and rich surface properties. However, bulk BaO still faces many challenges in practical applications: firstly, its specific surface area is limited, resulting in insufficient exposure of active sites; secondly, it is prone to aggregation during the reaction, leading to rapid activity decay; and thirdly, the means of regulating its structure and performance are limited, making it difficult to optimize specific reactions.
[0007] Existing technologies include research on supported molecular sieve catalysts. For example, CN113797957B discloses a catalyst supported by a mesoporous molecular sieve, its preparation method, and its application. The support is a mesoporous molecular sieve, and the active components include La, Ba, and Li. CN113797956A discloses a supported catalyst, its preparation method, and its application. The support is the mesoporous molecular sieve SBA-15, and the active components include La, Ba, and Li. CN116328826A discloses a barium-containing L molecular sieve, its preparation method, and its application, with a chemical composition of (0.03~0.1)BaO:(0.9~1.3)M2O:Al2O3:(5~8)SiO2, where M is K and / or Na. CN115385354A discloses a molecular sieve, its preparation method, and its application, with a composition such as "mSiO2·nAl2O3·pB2O3·qMO". x The schematic chemical composition shown in the figure includes MO. x These are heteroatom oxides; etc. However, no catalysts have been developed for PET saccharification technology in the prior art, and the molecular sieve support structure used in the above catalysts makes it difficult to achieve high dispersion and size control of BaO nanoparticles, resulting in poor catalytic performance even when molecular sieve catalysts supported on BaO nanoparticles are used to prepare them.
[0008] Therefore, how to construct highly dispersed nanoscale BaO-based catalysts through innovative material design strategies, while simultaneously addressing key issues such as easy aggregation and low accessibility of active sites, has become an important research direction for promoting the development of PET saccharification technology. Developing novel catalytic systems that combine high activity, excellent stability, and good economic efficiency is of significant scientific and practical value for achieving efficient chemical recycling of PET. Summary of the Invention
[0009] The purpose of this invention is to address at least one of the aforementioned problems by providing a monodisperse nanoscale BaO-supported MWW molecular sieve catalyst, its preparation method, and its application, thereby solving the problems of easy agglomeration and poor accessibility of active sites in existing BaO catalysts. This method achieves uniform dispersion of BaO particles at the nanoscale on the outer surface of the molecular sieve, thus exhibiting excellent catalytic activity and selectivity in the PET saccharification reaction.
[0010] The objective of this invention is achieved through the following technical solution: The first aspect of this invention discloses a monodisperse nanoscale BaO-supported MWW molecular sieve catalyst, wherein the catalyst uses MWW molecular sieve as a support and disperses BaO nanoparticles, wherein: The catalyst has a chemical composition of aBaO•bSiO2•cAl2O3, where b / c = 20-50 and b / a = 10-25; 90-95% of the barium species in BaO nanoparticles are monodisperse barium oxide nanoparticles, and the average size of BaO nanoparticles is in the nanometer range, with at least 90% of BaO nanoparticles dispersed on the outer surface of the molecular sieve. At least 80% of the crystals with the MWW topology in the MWW molecular sieve are layered nanosheets with a thickness of 2.5-20 nanometers. The total specific surface area of the catalyst is 300-500 m² 2 / g, the external specific surface area accounts for no less than 30% of the total specific surface area.
[0011] Preferably, the MWW molecular sieve is at least one of Cy4-MWW, MCM-36, SCM-1, and SL-MWW.
[0012] Preferably, the total pore volume of the catalyst is not less than 0.5 cubic centimeters / gram; or, The total specific surface area of the catalyst is not less than 350 square meters per gram; or, The catalyst has an external specific surface area of not less than 150 square meters per gram; or, The specific surface area of the catalyst accounts for no less than 35% of the total specific surface area.
[0013] Preferably, the total pore volume of the catalyst is 0.5-1.5 cubic centimeters / gram; or, The total specific surface area of the catalyst is 400-450 m² / g; or, The catalyst has an external specific surface area of 180-340 square meters per gram; or, The catalyst has an external specific surface area that accounts for 50-88% of the total specific surface area.
[0014] A second aspect of this invention discloses a method for preparing a monodisperse nanoscale BaO-supported MWW molecular sieve catalyst as described above, comprising the following steps: The barium source was ground and mixed with MWW molecular sieve, and then calcined in air to obtain the catalyst.
[0015] Preferably, the barium source is at least one selected from barium nitrate, barium acetate, barium chloride, and barium carbonate; The MWW molecular sieve has a chemical composition of bSiO2•cAl2O3, where b / c = 20-50; The specific surface area of the MWW molecular sieve is not less than 180m². 2 / g; The ratio of barium source to MWW molecular sieve is 5-20 mmol / g.
[0016] Preferably, the barium source is pre-ground for 10-60 minutes before being ground and mixed with the MWW molecular sieve.
[0017] Preferably, the grinding and mixing time is 10-90 minutes; The roasting temperature is 400-700℃; The roasting time is 4-10 hours.
[0018] The third aspect of this invention discloses the application of a monodisperse nanoscale BaO-supported MWW molecular sieve catalyst as described above in the polyester glycolysis reaction.
[0019] Preferably, the polyester includes polyethylene terephthalate (PET) and polybutylene terephthalate (PBT), specifically including PET powder, PET chopped strands, PET insulating fibers, PET film and PBT powder; The conditions for the glycolysis reaction include: a reaction temperature of 150-200℃, a reaction time of 0.5-2 hours, and a catalyst mass of 1-10% of the total mass of the polyester raw materials.
[0020] The working principle of this invention is as follows: The MWW-type zeolite (molecular sieve) used in this scheme has a unique layered structure with open spaces between the layers and a surface rich in silanol groups. These hydroxyl groups can form strong interactions with the barium precursor, providing uniform anchoring sites for the barium active component, effectively inhibiting the agglomeration and sintering of BaO nanoparticles during preparation and reaction, thereby achieving high dispersion and size control of BaO nanoparticles and significantly increasing the number of catalytic active sites.
[0021] Meanwhile, the layered confinement effect of MWW-type zeolite can stabilize highly dispersed BaO active sites, reduce the reaction energy barrier by efficiently activating ethylene glycol molecules and selectively breaking ester bonds in PET, improve catalytic conversion efficiency and product selectivity, and ensure that the catalyst has high activity, high stability and long service life.
[0022] Compared with the prior art, the present invention has the following beneficial effects: This invention utilizes the unique layered structure and abundant surface hydroxyl groups of the MWW zeolite carrier to achieve high dispersion and size control of BaO nanoparticles, significantly improving the glycolysis efficiency of PET and obtaining a high BHET monomer yield. The preparation method is simple and green, requiring no organic solvents, and is suitable for large-scale production. The catalyst exhibits good cycling stability and substrate universality, demonstrating excellent degradation performance for various polyesters. Among them, the glycolysis reaction of PET shows excellent catalytic activity and selectivity, with a BHET yield of over 98%. Attached Figure Description
[0023] Figure 1 The images show the XRD patterns of the Ba-MWW catalysts with monodisperse nanoscale BaO supported on MWW molecular sieves prepared in Example 1 and Comparative Examples 1-3.
[0024] Figure 2 These are the argon adsorption-desorption isotherms of the Ba-MWW catalysts with monodisperse nanoscale BaO supported MWW molecular sieves prepared in Example 1 and Comparative Examples 1-3.
[0025] Figure 3 These are TEM and HAADF-STEM images of the Ba-MWW catalyst with monodisperse nanoscale BaO supported on MWW molecular sieves prepared in Example 1. Detailed Implementation
[0026] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments.
[0027] The endpoints and any values of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values should be understood to include values close to these ranges or values. For numerical ranges, the endpoint values of the various ranges, the endpoint values of the various ranges and individual point values, and individual point values can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.
[0028] In the context of this specification, the term total specific surface area refers to the total area possessed by a unit mass of sample, including internal and external surface areas. Non-porous samples only have external surface area, such as silicate cement and some clay mineral powders; porous and multi-porous samples have both external and internal surface areas, such as asbestos fibers, diatomaceous earth, and molecular sieves. In porous and multi-porous samples, the surface area of pores with a diameter less than 2 nm is the internal surface area; the surface area after deducting the internal surface area is called the external surface area. The external surface area possessed by a unit mass of sample is the external specific surface area.
[0029] In the context of this specification, pore volume, also known as pore capacity, refers to the volume of pores per unit mass of porous material. Total pore volume refers to the volume of all pores per unit mass of molecular sieve (generally only pores with a channel diameter less than 50 nm are included). Micropore volume refers to the volume of all micropores per unit mass of molecular sieve (generally referring to pores with a channel diameter less than 2 nm).
[0030] This invention provides a monodisperse nanoscale BaO-supported MWW molecular sieve catalyst, which has a schematic chemical composition shown as “aBaO•bSiO2•cAl2O3”, wherein b / c=20-50 and b / a=10-25; more than 90% of the barium species supported by the molecular sieve are monodisperse nanoscale barium oxide (the average size of the BaO particles is in the nanoscale).
[0031] According to a preferred embodiment of the present invention, b / c = 20-30, b / a = 15-25; preferably, b / c = 25-28, b / a = 16-20.
[0032] According to a preferred embodiment of the present invention, 90-95% of the barium species on the molecular sieve are monodisperse nano-barium oxide.
[0033] In this invention, the content of barium species on the molecular sieve can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the mass fraction of barium species on the molecular sieve is 5-20% based on the total weight of the barium-loaded molecular sieve catalyst, preferably 7.5-10%.
[0034] According to a preferred embodiment of the present invention, more than 90% of the barium species on the molecular sieve are dispersed on the outer surface of the molecular sieve; preferably, 95% of the barium species are dispersed on the outer surface of the molecular sieve, and are uniformly dispersed on the outer surface of the molecular sieve as nano-sized barium oxide.
[0035] According to a preferred embodiment of the present invention, in the molecular sieve, more than 80% of the crystals having the MWW topology are layered nanosheets. The thickness of the layered nanosheets can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the present invention. According to a preferred embodiment of the present invention, the thickness of the layered nanosheets is 2.5-20 nanometers.
[0036] According to a preferred embodiment of the present invention, the MWW molecular sieve used as the carrier may be at least one of Cy4-MWW, MCM-36, SCM-1, and SL-MWW, and preferably Cy4-MWW. It should be noted that Cy4-MWW can also be called CYC4-MWW. This scheme uses the Cy4-MWW prepared in Example 1 of the invention patent 202510921512X (MWW molecular sieve and its preparation method and application); specifically, in the direct hydrothermal synthesis of MWW molecular sieve, cyclobutanone (CYC4) is added, and the molar ratio of each raw material in the crystallization system is SiO2: Al2O3: Na2O: HMI: CYC4: H2O = 1: 0.033: 0.083: 0.3: 0.3: 18; the synthesis steps are as follows: first, 0.8g NaOH, 1.0g... NaAlO2 was added as the alkali source and aluminum source to 37.5g of deionized water, and stirred until clear. Then, 24.04g of silica sol (AS-40, solid content 40wt%), 4.77g of hexamethyleneimine, and 3.37g of cyclobutanone were added dropwise. After mixing the above substances evenly, the mixture was stirred at room temperature for 1 hour at 200 rpm. The resulting mixed sol was transferred to a 50mL polytetrafluoroethylene-lined, stainless steel hydrothermal reactor, sealed, and dynamically crystallized at 150℃ for 4 days at 26 rpm. After the synthesis was completed, the reactor was allowed to cool completely, and the resulting product was centrifuged, washed three times with deionized water, and then dried in an 80℃ oven to obtain the molecular sieve precursor Cy4-MWW. SL-MWW can also be called monolayer MWW, and its preparation method is based on invention patent CN110615446A (a method for one-step synthesis of monolayer MWW molecular sieves assisted by amphiphilic organosilane).
[0037] According to a preferred embodiment of the present invention, the total specific surface area of the catalyst is 300-500 m². 2 / g, the external specific surface area accounts for no less than 30% of the total specific surface area.
[0038] In this invention, the total pore volume of the molecular sieve can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the total pore volume of the catalyst is not less than 0.5 cubic centimeters / gram, preferably 0.5-1.5 cubic centimeters / gram, and more preferably 0.6-1.1 cubic centimeters / gram.
[0039] In this invention, the total specific surface area of the molecular sieve can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the total specific surface area of the catalyst is not less than 350 m² / g, preferably 400-450 m² / g, and more preferably 410-430 m² / g.
[0040] In this invention, the specific surface area of the molecular sieve can be selected from a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the specific surface area of the catalyst is not less than 150 m² / g, preferably 180-340 m² / g, and more preferably 200-300 m² / g.
[0041] In this invention, the ratio of the external specific surface area of the molecular sieve to the total specific surface area can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the ratio of the external specific surface area of the catalyst to the total specific surface area is not less than 35%, preferably 50-88%, and more preferably 50-60%.
[0042] Monodisperse nanoscale BaO-supported MWW molecular sieve catalysts with the aforementioned characteristics can all achieve the purpose of this invention. There are no special requirements for their preparation methods. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the preparation method of the monodisperse nanoscale BaO-supported MWW molecular sieve catalyst includes: pre-grinding a barium source thoroughly, then adding MWW molecular sieve and performing solid-state grinding for a certain period of time, and finally calcining in an air atmosphere.
[0043] In this invention, there are no special requirements for the ratio of barium source to MWW molecular sieve. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the ratio of barium source to MWW molecular sieve is 5-20 mmol / g, preferably 7.5-10 mmol / g.
[0044] In this invention, the range of barium sources that can be selected is relatively wide. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the barium source is an inorganic or organic divalent barium salt, preferably at least one of barium nitrate, barium acetate, barium chloride and barium carbonate, and more preferably barium nitrate.
[0045] In this invention, there are no special requirements for the type of mortar used for grinding. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the mortar is at least one of a suitable-sized quartz mortar, a silica mortar, or a metal mortar, preferably a quartz mortar.
[0046] In this invention, there are no special requirements for the SiO2 / Al2O3 molar ratio of the MWW molecular sieve. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the SiO2 / Al2O3 molar ratio of the MWW molecular sieve is 20-50, preferably 25-28.
[0047] In this invention, the time for barium source pre-grinding treatment can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of this invention. According to a preferred embodiment of this invention, the pre-grinding treatment time is 10-60 minutes, preferably 30-60 minutes.
[0048] In this invention, the grinding time for the barium source and MWW molecular sieve can be selected within a wide range. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the pre-grinding time is 10-90 minutes, preferably 20-40 minutes.
[0049] In this invention, there are no special requirements for the roasting temperature. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the roasting temperature is 400-700℃, preferably 500-600℃.
[0050] In this invention, there are no special requirements for the roasting time. The following is an illustrative description, but it does not limit the scope of the invention. According to a preferred embodiment of the invention, the roasting time is 4-10 hours, preferably 6-8 hours.
[0051] In this invention, there are no special requirements for the instruments and equipment used in the roasting process and for storing the catalyst. Commonly used roasting and drying equipment can be used in this invention and can be selected according to actual needs. For example, roasting can be carried out in a muffle furnace and storage can be carried out in a dryer.
[0052] According to a preferred embodiment of the present invention, the heating process during the roasting can be carried out according to the following steps: the muffle furnace is heated from 25°C to 200°C over 180 minutes (heating rate of about 1°C / min), then the temperature is maintained at 200°C for 2 hours, then the temperature is raised from 200°C to 400-700°C over 200-500 minutes (heating rate of about 1°C / min), and finally the temperature is maintained at 400-700°C for 6-10 hours.
[0053] The monodisperse nanoscale BaO-supported MWW molecular sieve catalyst prepared by the preparation method provided in this invention.
[0054] The present invention relates to the application of monodisperse nanoscale BaO-supported MWW molecular sieve catalysts in polyester glycolysis reactions. In these reactions, the catalysts of the present invention exhibit excellent catalytic properties for breaking polyester bonds, thereby enabling highly efficient glycolysis of polyester macromolecules.
[0055] The monodisperse nanoscale BaO supported MWW molecular sieve catalyst provided by this invention has more than 90% of the barium species dispersed on the outer surface of the molecular sieve, and 90-95% of the barium species are monodisperse nanoscale barium oxide.
[0056] This invention prepares a monodisperse nanoscale BaO-supported MWW molecular sieve catalyst via a solid-state metallization method. It utilizes readily available inorganic / organic barium salts, which are fully dispersed into MWW during solid-state grinding. The entire process is easy to operate and generates no toxic or harmful organic waste liquid. In the prepared monodisperse nanoscale BaO-supported MWW molecular sieve catalyst, over 90% of the barium species are dispersed on the outer surface of the molecular sieve, and over 90-95% of the barium species are monodisperse nanoscale barium oxide. This catalyst exhibits excellent catalytic activity in polyester glycolysis reactions.
[0057] The monodisperse nanoscale BaO-supported MWW molecular sieve catalyst provided by this invention is mainly used in polyester saccharification reactions. Further, the polyester mainly includes at least one of polyethylene terephthalate (PET) powder, chopped PET fibers, PET insulating fibers, PET film, and PBT powder; the saccharification reaction conditions include: a reaction temperature of 150-200℃, a reaction time of 0.5-2 hours, and a catalyst dosage of 1-10% of the polyester raw material mass.
[0058] In this invention, the total pore volume, total specific surface area, and external specific surface area of the catalyst were measured using the nitrogen physical adsorption-desorption method (BE method): the argon physical adsorption-desorption isotherm of the catalyst was measured using an Autosorb IQ 2 physical adsorption instrument, and then calculated using the BET equation and t-plot equation. The experimental conditions were: measurement temperature -196℃. Before measurement, the catalyst was pretreated in a vacuum at 300℃ for 7 hours.
[0059] In this invention, the XRD pattern of the catalyst was obtained using a Bruker D2 Advance X-ray powder diffractometer. The test conditions were: CuKα-ray source (λ=1.54Å), nickel filter, 2θ scan range 2~60°, operating voltage 30KV, current 10mA, and scan rate 5° / min. Before testing, the MWW molecular sieve catalyst was ground into powder using a mortar and pestle.
[0060] In this invention, the crystal structure characteristics of the catalyst are obtained by TEM images, which are measured using a transmission electron microscope (Tecnai G2 F20 S-Twi006 type transmission electron microscope, operating voltage 200kV).
[0061] In this invention, the barium supported on the molecular sieve and its content are detected by HAADF-STEM spectra, and the HAADF-STEM spectra of the catalyst are measured by aberration-corrected transmission electron microscopy (JEM-ARM300F, operating voltage 300kV).
[0062] In this invention, in the illustrative chemical composition of the catalyst “aBaO•bSiO2•cAl2O3”, a, b, and c represent the molar percentages, and the b / c and b / a ratios are determined by ICP-OES using an Agilent 5110 (OES) instrument.
[0063] Example 1 Monodisperse nanoscale BaO-supported MWW molecular sieve catalysts were prepared using a solid-state metallization method according to the following procedure: (1) Weigh 1.0g of barium nitrate, pour it into a mortar, and grind it thoroughly at room temperature for 30 minutes to obtain a finely ground barium source; (2) Using Cy4-MWW as a molecular sieve precursor, first weigh 0.5g of MWW molecular sieve precursor, then weigh 95mg of pre-ground barium source powder, place the zeolite precursor and barium nitrate together in a mortar, grind thoroughly for 30 minutes, and after they are completely mixed, transfer all the solids into a porcelain boat to obtain Ba-MWW molecular sieve precursor. The Ba-MWW molecular sieve precursor obtained in step (2) was placed in a muffle furnace. Under the condition of air introduction, the temperature was raised from 20°C to 200°C after 180 minutes (heating rate of about 1°C / min), then kept at 200°C for 2 hours, and then raised from 200°C to 550°C after 350 minutes (heating rate of about 1°C / min). Finally, it was calcined at 550°C in air for 6 hours to obtain a monodisperse nanoscale BaO supported MWW molecular sieve Ba-MWW molecular sieve catalyst.
[0064] The XRD results of the prepared Ba-MWW molecular sieve catalyst are shown in the figure. Figure 1 The BET results for Ba-MWW molecular sieves are shown in [the table below]. Figure 2 TEM and HAADF-STEM results of Ba-MWW molecular sieves are shown in [Figure 1]. Figure 3 .from Figure 1 The XRD results showed characteristic peaks of nano-BaO (2θ=24.3°) and maintained the characteristic peaks of the MWW framework; Figure 2The adsorption-desorption hysteresis loop shown exhibits the characteristic H3 hysteresis of typical two-dimensional layered materials; furthermore... Figure 3 TEM images showed uniformly dispersed nanoscale particles. These results indicate the successful preparation of a monodisperse nanoscale Ba-MWW molecular sieve catalyst. The prepared monodisperse nanoscale Ba-MWW molecular sieve catalyst has a silicon-to-aluminum ratio (SiO2 / Al2O3 molar ratio) of 28.6, a silicon-to-barium ratio (SiO2 / BaO molar ratio) of 16.2, a barium species mass fraction of 9.0%, a barium oxide nanoscale species content of 95% dispersed on the outer surface of the molecular sieve, 90% of the crystals with the MWW topology are layered nanosheets, and a total pore volume of 0.67 cm³. 3 / g, total specific surface area is 413.4m² 2 / g, external specific surface area is 206.9m² 2 / g, the external specific surface area accounts for 50% of the total specific surface area.
[0065] Example 2 The difference between this embodiment and Example 1 is that the molecular sieve precursor is changed to SCM-1.
[0066] The prepared catalyst has a silicon-to-aluminum ratio (SiO2 / Al2O3 molar ratio) of 23.2, a silicon-to-barium ratio (SiO2 / BaO molar ratio) of 14.9, a barium species mass fraction of 9.2%, a barium oxide nanoparticle content of 95% dispersed on the outer surface of the molecular sieve, and 90% of the crystals with the MWW topology are layered nanosheets with a total pore volume of 1.04 cm³. 3 / g, total specific surface area is 384.3m² 2 / g, external specific surface area is 230.4m² 2 / g, the external specific surface area accounts for 60% of the total specific surface area.
[0067] Example 3 The difference between this embodiment and Example 1 is that the molecular sieve precursor is changed to SL-MWW.
[0068] The prepared catalyst has a silicon-to-aluminum ratio (SiO2 / Al2O3 molar ratio) of 23.2, a silicon-to-barium ratio (SiO2 / BaO molar ratio) of 14.9, a barium species mass fraction of 9.2%, a barium oxide nanoparticle content of 90% dispersed on the outer surface of the molecular sieve, and 90% of the crystals with the MWW topology are layered nanosheets, with a total pore volume of 1.08 cm³. 3 / g, total specific surface area is 387.2m² 2 / g, external specific surface area is 340.4m² 2 / g, the external specific surface area accounts for 88% of the total specific surface area.
[0069] Example 4 The difference between this embodiment and Example 1 is that the molecular sieve precursor is changed to MCM-36.
[0070] The prepared catalyst has a silicon-to-aluminum ratio (SiO2 / Al2O3 molar ratio) of 21.0, a silicon-to-barium ratio (SiO2 / BaO molar ratio) of 15.6, a barium species mass fraction of 8.2%, a barium oxide nanoparticle content of 92% dispersed on the outer surface of the molecular sieve, and 95% of the crystals with the MWW topology are layered nanosheets with a total pore volume of 1.04 cm³. 3 / g, total specific surface area is 365.0m² 2 / g, external specific surface area is 305.1m² 2 / g, the external specific surface area accounts for 84% of the total specific surface area.
[0071] Example 5 The difference between this example and Example 1 is that the amount of barium nitrate used is 47.5 mg.
[0072] The prepared catalyst has a silicon-to-aluminum ratio (SiO2 / Al2O3 molar ratio) of 26.0, a silicon-to-barium ratio (SiO2 / BaO molar ratio) of 23.9, a barium species mass fraction of 6.1%, a barium oxide nanoparticle content of 90% dispersed on the outer surface of the molecular sieve, and 90% of the crystals with the MWW topology are layered nanosheets with a total pore volume of 0.75 cm³. 3 / g, total specific surface area is 422.6m² 2 / g, external specific surface area is 202.3m² 2 / g, the external specific surface area accounts for 48% of the total specific surface area.
[0073] Example 6 Compared with Example 1, the difference in this example is that the amount of barium nitrate used is 71.3 mg.
[0074] The prepared catalyst has a silicon-to-aluminum ratio (SiO2 / Al2O3 molar ratio) of 25.6, a silicon-to-barium ratio (SiO2 / BaO molar ratio) of 17.4, a barium species mass fraction of 8.0%, a barium oxide nanoparticle content of 95% dispersed on the outer surface of the molecular sieve, and 90% of the crystals with the MWW topology are layered nanosheets with a total pore volume of 0.71 cm³. 3 / g, total specific surface area is 419.5m² 2 / g, external specific surface area is 207.8m² 2 / g, the external specific surface area accounts for 50% of the total specific surface area.
[0075] Example 7 The difference between this example and Example 1 is that the amount of barium nitrate used is 118.8 mg.
[0076] The prepared catalyst has a silicon-to-aluminum ratio (SiO2 / Al2O3 molar ratio) of 26.4, a silicon-to-barium ratio (SiO2 / BaO molar ratio) of 11.4, a barium species mass fraction of 12.4%, a barium oxide nanoparticle content of 90% dispersed on the outer surface of the molecular sieve, and 90% of the crystals with the MWW topology are layered nanosheets with a total pore volume of 0.61 cm³. 3 / g, total specific surface area is 407.2m² 2 / g, external specific surface area is 214.1m² 2 / g, the external specific surface area accounts for 52.5% of the total specific surface area.
[0077] Comparative Example 1 Compared to Example 1, this comparative example differs in that no barium source is added.
[0078] The prepared catalyst has a silicon-to-aluminum ratio (SiO2 / Al2O3 molar ratio) of 24.4, a silicon-to-barium ratio (SiO2 / BaO molar ratio) of 0%, a content of 0% barium oxide nanoparticles dispersed on the outer surface of the molecular sieve, 90% of the crystals with the MWW topology are layered nanosheets, the thickness of the layered nanosheets is 9 nm, and the total pore volume is 0.79 cm³. 3 / g, total specific surface area is 476.8m² 2 / g, external specific surface area is 199.9m² 2 / g, the external specific surface area accounts for 42% of the total specific surface area.
[0079] Comparative Example 2 The difference between this comparative example and Example 1 is that the molecular sieve precursor is MCM-22.
[0080] The prepared catalyst has a silicon-to-aluminum ratio (SiO2 / Al2O3 molar ratio) of 26.6, a silicon-to-barium ratio (SiO2 / BaO molar ratio) of 20.3, a content of 50% barium oxide nanoparticles dispersed on the outer surface of the molecular sieve, 90% of the crystals with the MWW topology are layered nanosheets, the thickness of the layered nanosheets is 22.5 nm, and the total pore volume is 0.53 cm³. 3 / g, total specific surface area is 410.4m² 2 / g, external specific surface area is 150.6m² 2 / g, the external specific surface area accounts for 37% of the total specific surface area.
[0081] Comparative Example 3 Unlike Comparative Example 2, this comparative example does not include a barium source.
[0082] The prepared catalyst has a silicon-to-aluminum ratio (SiO2 / Al2O3 molar ratio) of 23.0, a silicon-to-barium ratio (SiO2 / BaO molar ratio) of 0%, a content of 0% barium oxide nanoparticles dispersed on the outer surface of the molecular sieve, and 90% of the crystals with the MWW topology are layered nanosheets with a thickness of 22.5 nm and a total pore volume of 0.53 cm³. 3 / g, total specific surface area is 454.3m² 2 / g, external specific surface area is 127.0m² 2 / g, the external specific surface area accounts for 27% of the total specific surface area.
[0083] Comparative Example 4 Compared with Example 1, this comparative example differs in that the metal loading method is ion exchange, prepared according to the steps reported in the literature [Applied Catalysis B: Environmental, 168-169, (2015), 531–539].
[0084] The prepared catalyst has a silicon-to-aluminum ratio (SiO2 / Al2O3 molar ratio) of 25.8, a silicon-to-barium ratio (SiO2 / BaO molar ratio) of 18.8, a content of 20% barium oxide nanoparticles dispersed on the outer surface of the molecular sieve, 92% of the crystals with the MWW topology are layered nanosheets, the thickness of the layered nanosheets is 9 nm, and the total pore volume is 0.78 cm³. 3 / g, total specific surface area is 442.8m² 2 / g, external specific surface area is 198.3m² 2 / g, the external specific surface area accounts for 45% of the total specific surface area.
[0085] Test Example 1 The performance of the Ba-MWW molecular sieve catalysts prepared in each embodiment and the catalysts prepared in the comparative example were evaluated for their glycolysis reaction properties with polyester PET powder, and the following steps were followed: Accurately weigh 100 mg of PET powder sample, mix it thoroughly with 5 mL of ethylene glycol and an appropriate amount of catalyst, and react at 195 °C for a specified time. After the reaction is complete, cool the system to room temperature, and transfer 100 μL of the reaction solution to 400 μL of deuterated dimethyl sulfoxide (DMSO-d6) for further processing. 1 H-NMR testing. BHET monomer yield was obtained through H-NMR analysis. 1Quantitative analysis was performed using ¹H-NMR combined with external standard curve analysis. Since the signals from the solvent ethylene glycol at δ=4.4 and 3.4 (attributed to hydroxyl and methylene protons, respectively) overlapped with the proton signals in the non-aromatic region of BHET, the characteristic peak of the BHET benzene ring protons (δ=8.13, singlet, 4H) was selected as the integration criterion to avoid interference. To separate and purify the product, the remaining mixture was diluted with an appropriate amount of water and recrystallized overnight at low temperature. The solid product was then collected by filtration and dried to obtain pure BHET monomer. The results are listed in Table 1.
[0086] Table 1 Results of Test Example 1 Table 1 shows that the BHET yields from PET saccharification using Cy-MWW and MCM-22 molecular sieve supports were only 10.2% and 7.9%, respectively. However, the Ba-MWW molecular sieve catalyst supported on monodisperse nano-sized barium oxide could effectively and completely convert PET powder, with the highest BHET yield reaching 98.1%. This indicates that the Ba-MWW molecular sieve catalyst supported on monodisperse nano-sized BaO exhibits excellent catalytic activity in the reaction with PET powder, which may be closely related to the highly dispersed, ultra-small size and good catalytic site accessibility of its nano-sized barium oxide. Comparative Example 2, using MCM-22 as the MWW support, although possessing the MWW topology, suffers from insufficient surface hydroxyl groups and anchoring sites, making it difficult to effectively disperse and confine BaO, resulting in larger BaO particle size and higher crystallinity. Figure 1 The XRD results further confirmed that this sample exhibited more significant BaO crystal phase characteristic peaks (2θ = 24.3°), indicating low exposure and poor accessibility of active sites, thus resulting in a significant decrease in catalytic activity and a BHET yield of 45.2%. Furthermore, in Comparative Example 4, barium species were supported using a traditional ion exchange method, resulting in a catalyst with only 20% nano-barium oxide species on the outer surface, with the vast majority of barium existing in ionic form within the molecular sieve channels or framework. The catalytic activity of ionic barium species is far lower than that of nano-barium oxide, making it difficult to effectively activate PET ester bonds and ethylene glycol, thus leading to poor overall catalytic performance (approximately 33.0% BHET yield).
[0087] Test Example 2 The Ba-MWW molecular sieve catalyst prepared in Example 1 was evaluated for its performance in the glycolysis reaction of different real PET plastics. The test method was the same as in Example 1, and the results are listed in Table 2.
[0088] Table 2 Results of Test Example 2 As shown in Table 2, the monodisperse nanoscale BaO-supported MWW molecular sieve catalyst exhibits excellent substrate versatility. When used for the glycolysis of polybutylene terephthalate (PBT) and various commercial PET products (including insulating fibers, chopped fibers, and transparent films) from different sources and in different forms, it demonstrates excellent and stable catalytic performance. The BHET yield for PBT reaches 98.2%, and high yields of 94% to 96% are achieved for different forms of PET products. This indicates that the catalyst of this invention possesses excellent degradation efficiency and broad industrial application prospects for polyester materials with different chemical structures, molecular weights, and physical forms.
[0089] The above description of the embodiments is provided to enable those skilled in the art to understand and use the invention. It will be apparent to those skilled in the art that various modifications can be made to these embodiments, and the general principles described herein can be applied to other embodiments without inventive effort. Therefore, the present invention is not limited to the above embodiments, and any improvements and modifications made by those skilled in the art based on the disclosure of the present invention without departing from the scope of the invention should be within the protection scope of the present invention.
Claims
1. A monodisperse nanoscale BaO-supported MWW molecular sieve catalyst, characterized in that, The catalyst uses MWW molecular sieve as a support and disperses BaO nanoparticles, wherein: The catalyst has a chemical composition of aBaO•bSiO2•cAl2O3, where b / c = 20-50 and b / a = 10-25; 90-95% of the barium species in BaO nanoparticles are monodisperse barium oxide nanoparticles, and the average size of BaO nanoparticles is in the nanometer range, with at least 90% of BaO nanoparticles dispersed on the outer surface of the molecular sieve. At least 80% of the crystals with the MWW topology in the MWW molecular sieve are layered nanosheets with a thickness of 2.5-20 nanometers. The total specific surface area of the catalyst is 300-500 m 2 / g, and the ratio of the external specific surface area to the total specific surface area is not less than 30%.
2. The monodisperse nanoscale BaO-supported MWW molecular sieve catalyst according to claim 1, characterized in that, The MWW molecular sieve is at least one of Cy4-MWW, MCM-36, SCM-1, and SL-MWW.
3. The monodisperse nanoscale BaO-supported MWW molecular sieve catalyst according to claim 1, characterized in that, The total pore volume of the catalyst is not less than 0.5 cubic centimeters / gram; or, The total specific surface area of the catalyst is not less than 350 square meters per gram; or, The catalyst has an external specific surface area of not less than 150 square meters per gram; or, The specific surface area of the catalyst accounts for no less than 35% of the total specific surface area.
4. The monodisperse nanoscale BaO supported MWW molecular sieve catalyst according to claim 3, characterized in that, The total pore volume of the catalyst is 0.5-1.5 cubic centimeters / gram; or, The total specific surface area of the catalyst is 400-450 m² / g; or, The catalyst has an external specific surface area of 180-340 square meters per gram; or, The catalyst has an external specific surface area that accounts for 50-88% of the total specific surface area.
5. A method for preparing a monodisperse nanoscale BaO-supported MWW molecular sieve catalyst as described in any one of claims 1-4, characterized in that, Includes the following steps: The barium source was ground and mixed with MWW molecular sieve, and then calcined in air to obtain the catalyst.
6. The method for preparing a monodisperse nanoscale BaO-supported MWW molecular sieve catalyst according to claim 5, characterized in that, The barium source is at least one of barium nitrate, barium acetate, barium chloride, and barium carbonate; The MWW molecular sieve has a chemical composition of bSiO2•cAl2O3, where b / c = 20-50; The specific surface area of the MWW molecular sieve is not less than 180m². 2 / g; The ratio of barium source to MWW molecular sieve is 5-20 mmol / g.
7. The method for preparing a monodisperse nanoscale BaO-supported MWW molecular sieve catalyst according to claim 5, characterized in that, The barium source is pre-ground for 10-60 minutes and then ground and mixed with MWW molecular sieve.
8. The method for preparing a monodisperse nanoscale BaO-supported MWW molecular sieve catalyst according to claim 5, characterized in that, The grinding and mixing time is 10-90 minutes; The roasting temperature is 400-700℃; The roasting time is 4-10 hours.
9. The application of a monodisperse nanoscale BaO-supported MWW molecular sieve catalyst as described in any one of claims 1-4 in polyester saccharification reaction.
10. The application according to claim 8, characterized in that, The polyester includes polyethylene terephthalate and polybutylene terephthalate; The conditions for the glycolysis reaction include: a reaction temperature of 150-200℃, a reaction time of 0.5-2 hours, and a catalyst mass of 1-10% of the total mass of the polyester raw materials.