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2024 Volume 43 Issue 4
2024, 43(4): 100235
doi: 10.1016/j.cjsc.2024.100235
Abstract:
In conclusion, we successfully synthesize a novel ZLS, DNL-16, using 1,4-MPBOH as the OSDA. The unique layered structure of DNL-16, characterized by bre CBUs, is intricately unraveled using 3D ED. Further, the precise location of 1,4-MPBOH, situated between adjacent L0 layers of DNL-16, is determined through high-quality PXRD complemented by Rietveld refinement. These findings not only reveal the complex structure of DNL-16 but also lay a foundational groundwork for future investigations into its potential applications.
In conclusion, we successfully synthesize a novel ZLS, DNL-16, using 1,4-MPBOH as the OSDA. The unique layered structure of DNL-16, characterized by bre CBUs, is intricately unraveled using 3D ED. Further, the precise location of 1,4-MPBOH, situated between adjacent L0 layers of DNL-16, is determined through high-quality PXRD complemented by Rietveld refinement. These findings not only reveal the complex structure of DNL-16 but also lay a foundational groundwork for future investigations into its potential applications.
2024, 43(4): 100237
doi: 10.1016/j.cjsc.2024.100237
Abstract:
Zeolites have received great attention due to their wide applications in various fields such as catalysis, adsorption/separation, ion exchange, etc. Determining the atomic crystal structure of zeolites is crucial to understanding their functions and exploring their applications. Due to the difficulty of synthesizing large single crystals, the structures of many zeolites cannot be solved using conventional single-crystal X-ray diffraction (SCXRD) methods. Three-dimensional electron diffraction (3D ED) has witnessed rapid development during the past decade and has shown its powerful ability in the structure determination of zeolites. In this review, we will briefly introduce the history of 3D ED and summarize recent advances in the application of 3D ED for the analysis of zeolite structures, along with several typical examples in this research field.
Zeolites have received great attention due to their wide applications in various fields such as catalysis, adsorption/separation, ion exchange, etc. Determining the atomic crystal structure of zeolites is crucial to understanding their functions and exploring their applications. Due to the difficulty of synthesizing large single crystals, the structures of many zeolites cannot be solved using conventional single-crystal X-ray diffraction (SCXRD) methods. Three-dimensional electron diffraction (3D ED) has witnessed rapid development during the past decade and has shown its powerful ability in the structure determination of zeolites. In this review, we will briefly introduce the history of 3D ED and summarize recent advances in the application of 3D ED for the analysis of zeolite structures, along with several typical examples in this research field.
2024, 43(4): 100247
doi: 10.1016/j.cjsc.2024.100247
Abstract:
MOR zeolite has been effectively utilized for dimethyl ether (DME) carbonylation reaction due to its unique pore structure and acidity. During industrial production, the transformation of ammonium type MOR zeolite (NH4-MOR) into proton type MOR zeolite (H-MOR) causes inevitable dealumination. Therefore, understanding the influencing factors and dynamic evolution mechanism of zeolite dealumination is crucial. In this work, the stability of framework aluminum was studied by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, 29Si, 27Al, 1H magic angle spinning nuclear magnetic resonance (MAS NMR), and DME carbonylation performance evaluation. These results indicate that extra-framework cation Na+ and NH4+ could better preserve the aluminum structure of the MOR zeolite framework compared to H+, primarily due to the different ‘attraction’ of the framework to water. Furthermore, the impact of water on the zeolite framework aluminum at high temperature was studied by manipulating the humidity of the calcination atmosphere, revealing the formation of extra-framework six-coordinated aluminum (Al(VI)-EF) and the mechanism of water influence on the zeolite framework aluminum.
MOR zeolite has been effectively utilized for dimethyl ether (DME) carbonylation reaction due to its unique pore structure and acidity. During industrial production, the transformation of ammonium type MOR zeolite (NH4-MOR) into proton type MOR zeolite (H-MOR) causes inevitable dealumination. Therefore, understanding the influencing factors and dynamic evolution mechanism of zeolite dealumination is crucial. In this work, the stability of framework aluminum was studied by X-ray diffraction (XRD), Fourier transform infrared (FT-IR) spectroscopy, 29Si, 27Al, 1H magic angle spinning nuclear magnetic resonance (MAS NMR), and DME carbonylation performance evaluation. These results indicate that extra-framework cation Na+ and NH4+ could better preserve the aluminum structure of the MOR zeolite framework compared to H+, primarily due to the different ‘attraction’ of the framework to water. Furthermore, the impact of water on the zeolite framework aluminum at high temperature was studied by manipulating the humidity of the calcination atmosphere, revealing the formation of extra-framework six-coordinated aluminum (Al(VI)-EF) and the mechanism of water influence on the zeolite framework aluminum.
2024, 43(4): 100248
doi: 10.1016/j.cjsc.2024.100248
Abstract:
Highly dispersed and stable Pt-based catalysts play a crucial role in constructing efficient catalytic systems for alkane dehydrogenation. In this study, a novel bimetallic Pt–Sn catalyst confined in extra-large-pore ECNU-46 zeolite (denoted as Pt/Sn-ECNU-46) is prepared by post-treatment. The open-site framework Sn species ((SiO)3Sn–OH) serve as anchors to interact with Pt species, favoring the high dispersion of Pt. On the other hand, the framework Sn species act as the second metal to regulate the geometrical and electronic environment of Pt species, thus suppressing their accumulation. Pt/Sn-ECNU-46 achieves a good performance in propane dehydrogenation (PDH) reaction with high initial propane conversion (46%) and propylene selectivity (> 99%) as well as regeneration ability. In addition, Pt/Sn-ECNU-46 is also active in the dehydrogenation of n-hexane. This study explores the application of extra-large-pore zeolite as support in constructing metal-confined catalysts for alkane dehydrogenation.
Highly dispersed and stable Pt-based catalysts play a crucial role in constructing efficient catalytic systems for alkane dehydrogenation. In this study, a novel bimetallic Pt–Sn catalyst confined in extra-large-pore ECNU-46 zeolite (denoted as Pt/Sn-ECNU-46) is prepared by post-treatment. The open-site framework Sn species ((SiO)3Sn–OH) serve as anchors to interact with Pt species, favoring the high dispersion of Pt. On the other hand, the framework Sn species act as the second metal to regulate the geometrical and electronic environment of Pt species, thus suppressing their accumulation. Pt/Sn-ECNU-46 achieves a good performance in propane dehydrogenation (PDH) reaction with high initial propane conversion (46%) and propylene selectivity (> 99%) as well as regeneration ability. In addition, Pt/Sn-ECNU-46 is also active in the dehydrogenation of n-hexane. This study explores the application of extra-large-pore zeolite as support in constructing metal-confined catalysts for alkane dehydrogenation.
2024, 43(4): 100250
doi: 10.1016/j.cjsc.2024.100250
Abstract:
Zeolite is one of the most important heterogeneous catalysts in acid catalytic reactions. Considering that the catalytic behaviors of zeolites are mostly related to their acidic characteristics, extensive attention has been attracted to the measurements of acid type, strength and concentration in zeolites. Numerous techniques including Fourier-transform infrared (FTIR) spectroscopy, probe-assisted 1H, 13C and 31P magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR) as well as temperature programmed desorption of ammonia (NH3-TPD) have been developed for determining the acid sites. Nevertheless, a single approach is defective to characterize the acid sites comprehensively. Herein, combining the probe-assisted (e.g., NH3 and CD3CN) 1H MAS NMR and NH3-TPD, the acid sites in different zeolites including the acid type, density and strength were determined. The commonly utilized NH3-TPD to determine the acid strength of zeolite samples with different topologies should be rigorously considered owing to zeolite confinement effect. Controlling the desorption temperature of NH3 probe molecules, the acid type (i.e., Brønsted acid sites (BAS) and Lewis acid sites (LAS)) and the corresponding density could be determined by NH3 probe-assisted 1H MAS NMR spectroscopy, while the acid strength could be investigated via CD3CN probe-assisted 1H MAS NMR spectroscopy.
Zeolite is one of the most important heterogeneous catalysts in acid catalytic reactions. Considering that the catalytic behaviors of zeolites are mostly related to their acidic characteristics, extensive attention has been attracted to the measurements of acid type, strength and concentration in zeolites. Numerous techniques including Fourier-transform infrared (FTIR) spectroscopy, probe-assisted 1H, 13C and 31P magic angle spinning nuclear magnetic resonance spectroscopy (MAS NMR) as well as temperature programmed desorption of ammonia (NH3-TPD) have been developed for determining the acid sites. Nevertheless, a single approach is defective to characterize the acid sites comprehensively. Herein, combining the probe-assisted (e.g., NH3 and CD3CN) 1H MAS NMR and NH3-TPD, the acid sites in different zeolites including the acid type, density and strength were determined. The commonly utilized NH3-TPD to determine the acid strength of zeolite samples with different topologies should be rigorously considered owing to zeolite confinement effect. Controlling the desorption temperature of NH3 probe molecules, the acid type (i.e., Brønsted acid sites (BAS) and Lewis acid sites (LAS)) and the corresponding density could be determined by NH3 probe-assisted 1H MAS NMR spectroscopy, while the acid strength could be investigated via CD3CN probe-assisted 1H MAS NMR spectroscopy.
2024, 43(4): 100252
doi: 10.1016/j.cjsc.2024.100252
Abstract:
Though zeolites have been successfully synthesized for several decades, the roles of templates for zeolite synthesis are still not fully understood yet. Currently, many types of templates have been employed such as inorganic alkali metal ions, organic quaternary ammonium cations, organic amines, organic quaternary phosphonium cations, metal complexes and zeolite seeds, and the roles are mainly summarized into three aspects: structure-directing, space-filling and charge-balancing. In order to synthesize zeolites efficiently, the proposed principles to guide zeolite synthesis are the stabilization of energy between templates and zeolite framework, charge density mismatching (CDM) and structure matching between zeolite frameworks and templates. The purpose of this review is to briefly summarize the progresses in recent years, clearly showing the roles of the templates for zeolite synthesis.
Though zeolites have been successfully synthesized for several decades, the roles of templates for zeolite synthesis are still not fully understood yet. Currently, many types of templates have been employed such as inorganic alkali metal ions, organic quaternary ammonium cations, organic amines, organic quaternary phosphonium cations, metal complexes and zeolite seeds, and the roles are mainly summarized into three aspects: structure-directing, space-filling and charge-balancing. In order to synthesize zeolites efficiently, the proposed principles to guide zeolite synthesis are the stabilization of energy between templates and zeolite framework, charge density mismatching (CDM) and structure matching between zeolite frameworks and templates. The purpose of this review is to briefly summarize the progresses in recent years, clearly showing the roles of the templates for zeolite synthesis.
2024, 43(4): 100265
doi: 10.1016/j.cjsc.2024.100265
Abstract:
In the context of heightened environmental consciousness and the growing demand for light olefins, this study explores the promising future prospects for their sustainable production from renewable resources. Light olefins (especially propylene) are a pivotal constituent of the petrochemical industry, and their demand is poised for steady growth driven by various sectors (e.g., electric mobility, consumer goods and packaging industries), which should not rely solely on traditional petroleum-led routes. Therefore, sustainable pathways, such as the methanol-to-olefin (MTO) process catalyzed by zeolites, are gaining attention. Intending to couple the future olefin demands with the concept of a “methanol economy”, this study investigates the synthesis of hierarchical Ca/ZSM-5 zeolites using a cost-effective approach involving Precipitated Calcium Carbonate (PCC) as a hard template, leading to superior catalytic performance. Comprehensive characterization techniques are employed to elucidate the catalyst's properties, highlighting the dual importance of mesoporosity and calcium species in optimizing its performance. Operando spectroscopy provides in-depth insights into its enhanced anti-coking characteristics. This research contributes to expanding the catalyst toolkit for zeolite-catalyzed MTO processes, focusing on propylene production, thereby addressing the increasing demand for light olefins while promoting sustainability and circular economy principles.
In the context of heightened environmental consciousness and the growing demand for light olefins, this study explores the promising future prospects for their sustainable production from renewable resources. Light olefins (especially propylene) are a pivotal constituent of the petrochemical industry, and their demand is poised for steady growth driven by various sectors (e.g., electric mobility, consumer goods and packaging industries), which should not rely solely on traditional petroleum-led routes. Therefore, sustainable pathways, such as the methanol-to-olefin (MTO) process catalyzed by zeolites, are gaining attention. Intending to couple the future olefin demands with the concept of a “methanol economy”, this study investigates the synthesis of hierarchical Ca/ZSM-5 zeolites using a cost-effective approach involving Precipitated Calcium Carbonate (PCC) as a hard template, leading to superior catalytic performance. Comprehensive characterization techniques are employed to elucidate the catalyst's properties, highlighting the dual importance of mesoporosity and calcium species in optimizing its performance. Operando spectroscopy provides in-depth insights into its enhanced anti-coking characteristics. This research contributes to expanding the catalyst toolkit for zeolite-catalyzed MTO processes, focusing on propylene production, thereby addressing the increasing demand for light olefins while promoting sustainability and circular economy principles.
