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Walenszus F, Bon V, Evans JD, Krause S, Getzschmann J, Kaskel S, Dvoyashkin M. On the role of history-dependent adsorbate distribution and metastable states in switchable mesoporous metal-organic frameworks. Nat Commun 2023; 14:3223. [PMID: 37270577 DOI: 10.1038/s41467-023-38737-6] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/09/2022] [Accepted: 05/10/2023] [Indexed: 06/05/2023] Open
Abstract
A unique feature of metal-organic frameworks (MOFs) in contrast to rigid nanoporous materials is their structural switchabilty offering a wide range of functionality for sustainable energy storage, separation and sensing applications. This has initiated a series of experimental and theoretical studies predominantly aiming at understanding the thermodynamic conditions to transform and release gas, but the nature of sorption-induced switching transitions remains poorly understood. Here we report experimental evidence for fluid metastability and history-dependent states during sorption triggering the structural change of the framework and leading to the counterintuitive phenomenon of negative gas adsorption (NGA) in flexible MOFs. Preparation of two isoreticular MOFs differing by structural flexibility and performing direct in situ diffusion studies aided by in situ X-ray diffraction, scanning electron microscopy and computational modelling, allowed assessment of n-butane molecular dynamics, phase state, and the framework response to obtain a microscopic picture for each step of the sorption process.
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Affiliation(s)
- Francesco Walenszus
- Department of Inorganic Chemistry, Technische Universität Dresden, 01069, Dresden, Germany
| | - Volodymyr Bon
- Department of Inorganic Chemistry, Technische Universität Dresden, 01069, Dresden, Germany
| | - Jack D Evans
- Centre for Advanced Nanomaterials and Department of Chemistry, The University of Adelaide, Adelaide, SA, 5000, Australia
| | - Simon Krause
- Nanochemistry department, Max Planck Institute for Solid State Research, 70569, Stuttgart, Germany
| | - Jürgen Getzschmann
- Department of Inorganic Chemistry, Technische Universität Dresden, 01069, Dresden, Germany
| | - Stefan Kaskel
- Department of Inorganic Chemistry, Technische Universität Dresden, 01069, Dresden, Germany.
- Fraunhofer Institute IWS, Winterbergstr. 28, 01277, Dresden, Germany.
| | - Muslim Dvoyashkin
- Institute of Chemical Technology, Universität Leipzig, 04103, Leipzig, Germany.
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Walenszus F, Bon V, Evans JD, Kaskel S, Dvoyashkin M. Molecular Diffusion in a Flexible Mesoporous Metal-Organic Framework over the Course of Structural Contraction. J Phys Chem Lett 2020; 11:9696-9701. [PMID: 33136403 PMCID: PMC9115798 DOI: 10.1021/acs.jpclett.0c02745] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/09/2020] [Accepted: 10/21/2020] [Indexed: 06/05/2023]
Abstract
In situ 1H pulsed field gradient (PFG) NMR was used to investigate the molecular diffusion of n-butane in the pores of the flexible metal-organic framework DUT-49(Cu) at 298 K at different pore loadings, including pressure ranges below and above the negative gas adsorption (NGA) transition caused by structural contraction of the material. Supported by molecular dynamics simulations, the investigation provided crucial insight into confined diffusion within a highly flexible pore environment. The self-diffusion coefficients were derived from the experiment and compared with simulations, capturing the diffusion during n-butane adsorption and desorption. This complementary approach has yielded experimental characterization of molecular diffusion mechanisms during the unique process of NGA. This includes the observation of a 4-fold decrease of diffusivity within a less than 2 kPa gas pressure variation, corresponding to the NGA transition point.
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Affiliation(s)
- Francesco Walenszus
- Department
of Inorganic Chemistry, Technische Universität
Dresden, 01069 Dresden, Germany
| | - Volodymyr Bon
- Department
of Inorganic Chemistry, Technische Universität
Dresden, 01069 Dresden, Germany
| | - Jack D. Evans
- Department
of Inorganic Chemistry, Technische Universität
Dresden, 01069 Dresden, Germany
| | - Stefan Kaskel
- Department
of Inorganic Chemistry, Technische Universität
Dresden, 01069 Dresden, Germany
| | - Muslim Dvoyashkin
- Institute
of Chemical Technology, Universität
Leipzig, 04103 Leipzig, Germany
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Zaheer MA, Poppitz D, Feyzullayeva K, Wenzel M, Matysik J, Ljupkovic R, Zarubica A, Karavaev AA, Pöppl A, Gläser R, Dvoyashkin M. Synthesis of highly active ETS-10-based titanosilicate for heterogeneously catalyzed transesterification of triglycerides. Beilstein J Nanotechnol 2019; 10:2039-2061. [PMID: 31728253 PMCID: PMC6839565 DOI: 10.3762/bjnano.10.200] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Figures] [Subscribe] [Scholar Register] [Received: 07/15/2019] [Accepted: 10/15/2019] [Indexed: 06/10/2023]
Abstract
In this contribution, the preparation of hierarchically structured ETS-10-based catalysts exhibiting notably higher activity in the conversion of triolein with methanol compared to microporous titanosilicate is presented. Triolein, together with its unsaturated analog trilinolein, represent the most prevalent triglycerides in oils. The introduction of mesopores by post-synthetic treatment with hydrogen peroxide and a subsequent calcination step results in the generation of an additional active surface with Brønsted basic sites becoming accessible for triolein and enhancing the rate of transesterification. The resulting catalyst exhibits a comparable triolein conversion (≈73%) after 4 h of reaction to CaO (≈76%), which is reportedly known to be highly active in the transesterification of triglycerides. In addition, while CaO showed a maximum conversion of 83% after 24 h, the ETS-10-based catalyst reached 100% after 8 h, revealing its higher stability compared to CaO. The following characteristics of the catalysts were experimentally addressed - crystal structure (X-ray diffraction, transmission electron microscopy), crystal shape and size (scanning electron microscopy, laser diffraction), textural properties (N2 sorption, Hg porosimetry), presence of hydroxyl groups and active sites (temperature-programmed desorption of NH3 and CO2, 29Si magic angle spinning nuclear magnetic resonance (NMR)), mesopore accessibility and diffusion coefficient of adsorbed triolein (pulsed field gradient NMR), pore interconnectivity (variable temperature and exchange spectroscopy experiments using hyperpolarized 129Xe NMR) and oxidation state of Ti atoms (electron paramagnetic resonance). The obtained results enabled the detailed understanding of the impact of the post-synthetic treatment applied to the ETS-10 titanosilicate with respect to the catalytic activity in the heterogeneously catalyzed transesterification of triglycerides.
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Affiliation(s)
- Muhammad A Zaheer
- Institute of Chemical Technology, Universität Leipzig, Linnéstraße 3, 04103 Leipzig, Germany
| | - David Poppitz
- Institute of Chemical Technology, Universität Leipzig, Linnéstraße 3, 04103 Leipzig, Germany
| | - Khavar Feyzullayeva
- Institute of Chemical Technology, Universität Leipzig, Linnéstraße 3, 04103 Leipzig, Germany
| | - Marianne Wenzel
- Institute of Analytical Chemistry, Universität Leipzig, Linnéstraße 3, 04103 Leipzig, Germany
| | - Jörg Matysik
- Institute of Analytical Chemistry, Universität Leipzig, Linnéstraße 3, 04103 Leipzig, Germany
| | - Radomir Ljupkovic
- Faculty of Science and Mathematics, University of Nis, Visegradska 33, 18000 Nis, Serbia
| | - Aleksandra Zarubica
- Faculty of Science and Mathematics, University of Nis, Visegradska 33, 18000 Nis, Serbia
| | - Alexander A Karavaev
- Gubkin Russian State University of Oil and Gas, Leninsky Prospekt 65, 119991 Moscow, Russia
| | - Andreas Pöppl
- Felix-Bloch-Institut, Universität Leipzig, Linnéstraße 5, 04103 Leipzig, Germany
| | - Roger Gläser
- Institute of Chemical Technology, Universität Leipzig, Linnéstraße 3, 04103 Leipzig, Germany
| | - Muslim Dvoyashkin
- Institute of Chemical Technology, Universität Leipzig, Linnéstraße 3, 04103 Leipzig, Germany
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Dvoyashkin M, Wilde N, Haase J, Gläser R. Correction: Diffusion of methyl oleate in hierarchical micro-/mesoporous TS-1-based catalysts probed by PFG NMR spectroscopy. RSC Adv 2018; 8:40060. [PMID: 35560832 PMCID: PMC9091422 DOI: 10.1039/c8ra90098a] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/27/2018] [Accepted: 11/27/2018] [Indexed: 11/21/2022] Open
Abstract
Correction for ‘Diffusion of methyl oleate in hierarchical micro-/mesoporous TS-1-based catalysts probed by PFG NMR spectroscopy’ by Muslim Dvoyashkin et al., RSC Adv., 2018, 8, 38941–38944.
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Affiliation(s)
- Muslim Dvoyashkin
- Institute of Chemical Technology
- Universität Leipzig
- 04103 Leipzig
- Germany
| | - Nicole Wilde
- Institute of Chemical Technology
- Universität Leipzig
- 04103 Leipzig
- Germany
| | - Jürgen Haase
- Felix-Bloch-Institut
- Universität Leipzig
- 04103 Leipzig
- Germany
| | - Roger Gläser
- Institute of Chemical Technology
- Universität Leipzig
- 04103 Leipzig
- Germany
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Dvoyashkin M, Wilde N, Haase J, Gläser R. Diffusion of methyl oleate in hierarchical micro-/mesoporous TS-1-based catalysts probed by PFG NMR spectroscopy. RSC Adv 2018; 8:38941-38944. [PMID: 35558297 PMCID: PMC9090670 DOI: 10.1039/c8ra07434h] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.3] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/06/2018] [Revised: 11/30/2018] [Accepted: 11/07/2018] [Indexed: 11/23/2022] Open
Abstract
Pulsed field gradient (PFG) NMR is successfully applied to trace the diffusion of methyl oleate (MO) inside the mesopores of hierarchically structured titanium silicalite-1 (TS-1)-based catalysts. Introduction of mesoporosity by post-synthetic treatment of initially microporous TS-1 provides additional active surface to improve catalytic activity in the epoxidation of MO. The present study provides experimental evidence of the accessibility of mesopores for MO resulting from alkaline treatment of TS-1. The self-diffusion coefficients of MO inside the pores of hierarchically structured TS-1 catalysts are up to two orders of magnitude lower compared to the values in the bulk liquid phase. Additionally, the methodological capability of PFG NMR for measuring self-diffusion coefficients of long-chain hydrocarbons (up to C19) confined to narrow mesopores of catalytically active is demonstrated for the first time. Direct assessment of methyl oleate diffusion confined to nanopores of TS-1-based catalysts by means of pulsed field gradient NMR.![]()
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Affiliation(s)
- Muslim Dvoyashkin
- Institute of Chemical Technology
- Universität Leipzig
- 04103 Leipzig
- Germany
| | - Nicole Wilde
- Institute of Chemical Technology
- Universität Leipzig
- 04103 Leipzig
- Germany
| | - Jürgen Haase
- Felix-Bloch-Institut
- Universität Leipzig
- 04103 Leipzig
- Germany
| | - Roger Gläser
- Institute of Chemical Technology
- Universität Leipzig
- 04103 Leipzig
- Germany
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Zaheer MA, Zill JC, Matysik J, Gläser R, Dvoyashkin M. In Situ and in Operando Characterization of Mixing Dynamics in Liquid-Phase Reactions by 129
Xe NMR Spectroscopy. Chemphyschem 2017; 18:1513-1516. [DOI: 10.1002/cphc.201700080] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/24/2017] [Revised: 03/02/2017] [Indexed: 11/11/2022]
Affiliation(s)
- Muhammad A. Zaheer
- Institute of Chemical Technology; Universität Leipzig; 04103 Leipzig Germany
| | - Jeremias C. Zill
- Institute of Analytical Chemistry; Universität Leipzig; 04103 Leipzig Germany
| | - Jörg Matysik
- Institute of Analytical Chemistry; Universität Leipzig; 04103 Leipzig Germany
| | - Roger Gläser
- Institute of Chemical Technology; Universität Leipzig; 04103 Leipzig Germany
| | - Muslim Dvoyashkin
- Institute of Chemical Technology; Universität Leipzig; 04103 Leipzig Germany
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Kalz KF, Kraehnert R, Dvoyashkin M, Dittmeyer R, Gläser R, Krewer U, Reuter K, Grunwaldt J. Future Challenges in Heterogeneous Catalysis: Understanding Catalysts under Dynamic Reaction Conditions. ChemCatChem 2017; 9:17-29. [PMID: 28239429 PMCID: PMC5299475 DOI: 10.1002/cctc.201600996] [Citation(s) in RCA: 195] [Impact Index Per Article: 27.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/11/2016] [Indexed: 01/12/2023]
Abstract
In the future, (electro-)chemical catalysts will have to be more tolerant towards a varying supply of energy and raw materials. This is mainly due to the fluctuating nature of renewable energies. For example, power-to-chemical processes require a shift from steady-state operation towards operation under dynamic reaction conditions. This brings along a number of demands for the design of both catalysts and reactors, because it is well-known that the structure of catalysts is very dynamic. However, in-depth studies of catalysts and catalytic reactors under such transient conditions have only started recently. This requires studies and advances in the fields of 1) operando spectroscopy including time-resolved methods, 2) theory with predictive quality, 3) kinetic modelling, 4) design of catalysts by appropriate preparation concepts, and 5) novel/modular reactor designs. An intensive exchange between these scientific disciplines will enable a substantial gain of fundamental knowledge which is urgently required. This concept article highlights recent developments, challenges, and future directions for understanding catalysts under dynamic reaction conditions.
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Affiliation(s)
- Kai F. Kalz
- Institute of Catalysis Research and Technology (IKFT)Karlsruhe Institute of Technology (KIT)D-76344Eggenstein-LeopoldshafenGermany
| | - Ralph Kraehnert
- Department of ChemistryTechnische Universität BerlinD-10623BerlinGermany
| | - Muslim Dvoyashkin
- Institute of Chemical TechnologyUniversität LeipzigD-04103LeipzigGermany
| | - Roland Dittmeyer
- Institute for Micro Process Engineering (IMVT)Karlsruhe Institute of Technology (KIT)D-76344Eggenstein-LeopoldshafenGermany
| | - Roger Gläser
- Institute of Chemical TechnologyUniversität LeipzigD-04103LeipzigGermany
| | - Ulrike Krewer
- Institute of Energy and Process Systems EngineeringTU BraunschweigD-38106BraunschweigGermany
| | - Karsten Reuter
- Chair for Theoretical Chemistry and Catalysis Research CenterTechnische Universität MünchenD-85747GarchingGermany
| | - Jan‐Dierk Grunwaldt
- Institute of Catalysis Research and Technology (IKFT)Karlsruhe Institute of Technology (KIT)D-76344Eggenstein-LeopoldshafenGermany
- Institute for Chemical Technology and Polymer Chemistry (ITCP)Karlsruhe Institute of Technology (KIT)D-76131KarlsruheGermany
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Abstract
One-dimensional nanochannels, hundreds of microns in persistence length but with elliptical cross-sectional dimensions of only ∼3.7 Å × 4.8 Å, are formed by the columnar assembly of phenylether bis-urea macrocycles. Hyperpolarized Xe-129 NMR is utilized to investigate the Xe atom packing and Xe diffusion inside the needle shaped crystals. The elliptical channel structure produces a Xe-129 powder pattern characteristic of an asymmetric chemical shift tensor extending to well over 300 ppm with respect to the gas phase, reflecting the highly anisotropic electronic environment and extreme confinement of the atom. Consistent with the simple geometrical criterion, hyperpolarized tracer exchange NMR data reveals single-file diffusion in the bis-urea nanochannels.
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Affiliation(s)
- Clifford R. Bowers
- Department of Chemistry, University of Florida, Gainesville, FL 32611, USA
| | - Muslim Dvoyashkin
- Department of Chemistry, University of Florida, Gainesville, FL 32611, USA
| | - Sahan R. Salpage
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, USA
| | - Christopher Akel
- Department of Chemistry, University of Florida, Gainesville, FL 32611, USA
| | - Hrishi Bhase
- Department of Chemistry, University of Florida, Gainesville, FL 32611, USA
| | - Michael F. Geer
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, USA
| | - Linda S. Shimizu
- Department of Chemistry and Biochemistry, University of South Carolina, Columbia, SC 29208, USA
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Bowers CR, Dvoyashkin M, Salpage SR, Akel C, Bhase H, Geer MF, Shimizu LS. Crystalline Bis-urea Nanochannel Architectures Tailored for Single-File Diffusion Studies. ACS Nano 2015; 9:6343-6353. [PMID: 26035000 DOI: 10.1021/acsnano.5b01895] [Citation(s) in RCA: 8] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 06/04/2023]
Abstract
Urea is a versatile building block that can be modified to self-assemble into a multitude of structures. One-dimensional nanochannels with zigzag architecture and cross-sectional dimensions of only ∼3.7 Å × 4.8 Å are formed by the columnar assembly of phenyl ether bis-urea macrocycles. Nanochannels formed by phenylethynylene bis-urea macrocycles have a round cross-section with a diameter of ∼9.0 Å. This work compares the Xe atom packing and diffusion inside the crystalline channels of these two bis-ureas using hyperpolarized Xe-129 NMR. The elliptical channel structure of the phenyl ether bis-urea macrocycle produces a Xe-129 powder pattern line shape characteristic of an asymmetric chemical shift tensor with shifts extending to well over 300 ppm with respect to the bulk gas, reflecting extreme confinement of the Xe atom. The wider channels formed by phenylethynylene bis-urea, in contrast, present an isotropic dynamically average electronic environment. Completely different diffusion dynamics are revealed in the two bis-ureas using hyperpolarized spin-tracer exchange NMR. Thus, a simple replacement of phenyl ether with phenylethynylene as the rigid linker unit results in a transition from single-file to Fickian diffusion dynamics. Self-assembled bis-urea macrocycles are found to be highly suitable materials for fundamental molecular transport studies on micrometer length scales.
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Affiliation(s)
- Clifford R Bowers
- †Department of Chemistry, University of Florida, Gainesville, Florida 32611, United States
| | - Muslim Dvoyashkin
- †Department of Chemistry, University of Florida, Gainesville, Florida 32611, United States
| | - Sahan R Salpage
- ‡Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, United States
| | - Christopher Akel
- †Department of Chemistry, University of Florida, Gainesville, Florida 32611, United States
| | - Hrishi Bhase
- †Department of Chemistry, University of Florida, Gainesville, Florida 32611, United States
| | - Michael F Geer
- ‡Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, United States
| | - Linda S Shimizu
- ‡Department of Chemistry and Biochemistry, University of South Carolina, Columbia, South Carolina 29208, United States
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Dutta AR, Sekar P, Dvoyashkin M, Bowers CR, Ziegler KJ, Vasenkov S. Relationship between single-file diffusion of mixed and pure gases in dipeptide nanochannels by high field diffusion NMR. Chem Commun (Camb) 2015; 51:13346-9. [DOI: 10.1039/c5cc04960a] [Citation(s) in RCA: 7] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/17/2023]
Abstract
Under single-file confinement, the relationship between diffusion rates of mixed and pure gases is studied experimentally for the first time and observed to differ from that for normal diffusion.
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Affiliation(s)
- Akshita R. Dutta
- Department of Chemical Engineering
- University of Florida
- Gainesville
- USA
| | - Poorvajan Sekar
- Department of Chemical Engineering
- University of Florida
- Gainesville
- USA
| | | | | | - Kirk J. Ziegler
- Department of Chemical Engineering
- University of Florida
- Gainesville
- USA
| | - Sergey Vasenkov
- Department of Chemical Engineering
- University of Florida
- Gainesville
- USA
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Affiliation(s)
- Muslim Dvoyashkin
- Department
of Chemistry, University of Florida, Gainesville, Florida 32611, United States
| | - Hrishi Bhase
- Department
of Chemistry, University of Florida, Gainesville, Florida 32611, United States
| | - Navid Mirnazari
- Department
of Chemistry, University of Florida, Gainesville, Florida 32611, United States
| | - Sergey Vasenkov
- Department
of Chemical Engineering, University of Florida, Gainesville, Florida 32611, United States
| | - Clifford R. Bowers
- Department
of Chemistry, University of Florida, Gainesville, Florida 32611, United States
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Einicke WD, Enke D, Dvoyashkin M, Valiullin R, Gläser R. The Mechanism of Pseudomorphic Transformation of Spherical Silica Gel into MCM-41 Studied by PFG NMR Diffusometry. Materials (Basel) 2013; 6:3688-3709. [PMID: 28788300 PMCID: PMC5452651 DOI: 10.3390/ma6093688] [Citation(s) in RCA: 23] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 07/01/2013] [Revised: 08/16/2013] [Accepted: 08/19/2013] [Indexed: 11/20/2022]
Abstract
The pseudomorphic transformation of spherical silica gel (LiChrospher® Si 60) into MCM-41 was achieved by treatment at 383 K for 24 h with an aqueous solution of cetyltrimethylammonium hydroxide (CTAOH) instead of hexadecyltrimethylammonium bromide (CTABr) and NaOH. The degree of transformation was varied via the ratio of CTAOH solution to initial silica gel rather than synthesis duration. The transformed samples were characterized by N2 sorption at 77 K, mercury intrusion porosimetry, X-ray diffraction (XRD) and scanning electron microscopy (SEM). Thus, MCM-41 spheres with diameters of ca. 12 μm, surface areas >1000 m2 g−1, pore volumes >1 cm3 g−1 and a sharp pore width distribution, adjustable between 3.2 and 4.5 nm, were obtained. A thorough pulsed field gradient nuclear magnetic resonance (PFG NMR) study shows that the diffusivity of n-heptane confined in the pores of the solids passes through a minimum with progressing transformation. The final product of pseudomorphic transformation to MCM-41 does not exhibit improved transport properties compared to the initial silica gel. Moreover, the PFG NMR results support that the transformation occurs via formation and subsequent growth of domains of <1 μm containing MCM-41 homogeneously distributed over the volume of the silica spheres.
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Affiliation(s)
- Wolf-Dietrich Einicke
- Institute of Chemical Technology, Universität Leipzig, Linnéstr. 3, 04103 Leipzig, Germany.
| | - Dirk Enke
- Institute of Chemical Technology, Universität Leipzig, Linnéstr. 3, 04103 Leipzig, Germany.
| | - Muslim Dvoyashkin
- Institute of Experimental Physics I, Universität Leipzig, Linnéstr. 5, 04103 Leipzig, Germany.
| | - Rustem Valiullin
- Institute of Experimental Physics I, Universität Leipzig, Linnéstr. 5, 04103 Leipzig, Germany.
| | - Roger Gläser
- Institute of Chemical Technology, Universität Leipzig, Linnéstr. 3, 04103 Leipzig, Germany.
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Dvoyashkin M, Valiullin R, Kärger J, Einicke WD, Gläser R. Direct Assessment of Transport Properties of Supercritical Fluids Confined to Nanopores. J Am Chem Soc 2007; 129:10344-5. [PMID: 17672467 DOI: 10.1021/ja074101+] [Citation(s) in RCA: 31] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/28/2022]
Affiliation(s)
- Muslim Dvoyashkin
- Faculty of Physics and Geosciences, University of Leipzig, D-04103 Leipzig, Germany
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Dvoyashkin M, Valiullin R, Kärger J. Temperature effects on phase equilibrium and diffusion in mesopores. Phys Rev E Stat Nonlin Soft Matter Phys 2007; 75:041202. [PMID: 17500885 DOI: 10.1103/physreve.75.041202] [Citation(s) in RCA: 14] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 01/08/2007] [Revised: 02/21/2007] [Indexed: 05/15/2023]
Abstract
The equilibrium and dynamic properties of fluids confined to mesoporous material have been studied using nuclear magnetic resonance (NMR) methods. Molecular diffusion of n -pentane in Vycor porous glass within closed sample tubes has been measured by means of the pulsed field gradient (PFG) NMR method for temperatures notably exceeding the boiling point of the neat liquid. It is found that the temperature dependence of the diffusivity dramatically depends on the state of the fluid surrounding the mesoporous monoliths. In an oversaturated sample, i.e., in a sample containing some amount of the liquid also outside of the porous material, the diffusivity in the mesopores followed the Arrhenius dependence. In samples with only the mesopores saturated by the liquid, i.e., without any excess fluid, with increasing temperature the diffusivity notably deviated from the Arrhenius dependence towards higher diffusivities. The analysis of the intensities of the respective NMR signals from the fluid within the porous material and in the surrounding phase has revealed that this anomaly is accompanied by the formation of a space free of liquid within the pore system. With the measured pore filling factors, the resulting overall diffusivity is estimated by a two-region approach with diffusion occurring in either the liquid phase or the free space within the pore volume. It is shown that this procedure, free of any fitting parameters, yields excellent agreement with the experimental data.
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Affiliation(s)
- Muslim Dvoyashkin
- Fakultät für Physik und Geowissenschaften, Universität Leipzig, 04103 Leipzig, Germany
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Abstract
The pulsed field gradient nuclear magnetic resonance method has been used to study self-diffusion of cyclohexane in a commercial MCM-41 material at different external gas pressures from zero to saturated vapor pressure. It is found that the effective diffusivities exhibit three different regions with increasing pressure: decrease at low pressures, a sudden drop at intermediate pressures, and increase at higher pressures. In addition, in the region of irreversible adsorption (hysteresis loop) the diffusivities are also found to differ on the adsorption and the desorption branches. A simple analytical model taking account of different molecular ensembles with different transport properties due to the complex architecture of the porous structure is developed which provides a quantitative prediction of the experimental data. The analysis reveals that the effective diffusivity is predominantly controlled by the adsorption properties of the individual mesoporous MCM-41 crystallites which, in combination with high transport rates, provide a simple instrument for fine tuning of the transport properties by a subtle variation of the external conditions.
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Affiliation(s)
- Rustem Valiullin
- Fakultät für Physik und Geowissenschaften, Universität Leipzig, 04103 Leipzig, Germany.
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