| 1. |
- Creci, Simone, 1992, et al.
(författare)
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Acidity as Descriptor for Methanol Desorption in B-, Ga- and Ti-MFI Zeotypes
- 2021
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Ingår i: Catalysts. - : MDPI AG. - 2073-4344. ; 11:1, s. 1-12
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Tidskriftsartikel (refereegranskat)abstract
- The isomorphous substitution of Si with metals other than Al in zeotype frameworks allows for tuning the acidity of the zeotype and, therefore, to tailor the catalyst's properties as a function of the desired catalytic reaction. In this study, B, Ga, and Ti are incorporated in the MFI framework of silicalite samples and the following series of increasing acidity is observed: Ti-silicalite < B-silicalite < Ga-silicalite. It is also observed that the lower the acidity of the sample, the easier the methanol desorption from the zeotype surface. In the target reaction, namely the direct conversion of methane to methanol, methanol extraction is affected by the zeotype acidity. Therefore, the results shown in this study contribute to a more enriched knowledge of this reaction.
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| 2. |
- Creci, Simone, 1992, et al.
(författare)
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Methoxy ad-species in MFI zeotypes during methane exposure and methanol desorption followed by in situ IR spectroscopy
- 2021
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Ingår i: Catalysis Today. - : Elsevier BV. - 0920-5861. ; 369, s. 123-128
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Tidskriftsartikel (refereegranskat)abstract
- The formation and evolution of methoxy ad-species in MFI zeotypes after CH4 exposure, and during temperature programmed desorption of CH3OH have been investigated in situ with diffuse reflectance Fourier transform infrared spectroscopy. Fe and/or Al atoms have been incorporated in framework position prior to crystallization and the influence of the resulting acidity on CH4 activation and CH3OH desorption has been examined. The results show that the presence of Fe promotes CH4 activation and that methanol is more strongly bound to the zeotype in the presence of Al. Because CH4 activation and CH3OH extraction are two of the key steps in the direct conversion of methane to methanol, our results indicate that Al-free zeotypes containing Fe atoms pinpoint important catalyst design parameters needed for this reaction.
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| 3. |
- Danyliv, Olesia, et al.
(författare)
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Self-Standing, Robust Membranes Made of Cellulose Nanocrystals (CNCs) and a Protic Ionic Liquid : Toward Sustainable Electrolytes for Fuel Cells
- 2021
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Ingår i: ACS Applied Energy Materials. - : American Chemical Society. - 2574-0962. ; 4:7, s. 6474-6485
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Tidskriftsartikel (refereegranskat)abstract
- Energy-conversion devices based on the phenomenon of proton conduction, for example, polymer electrolyte membrane fuel cells (PEMFCs), require low cost and sustainable electrolytes with high ionic conductivity and good mechanical properties under anhydrous conditions and at temperatures up to 150 °C. Biopolymers possess an intrinsic thermomechanical stability but an insufficient proton conductivity in the dry state, which however may be imparted by a protic ionic liquid (PIL). This work presents the preparation and properties of composite membranes made of cellulose nanocrystals (CNCs) and a PIL. The membranes are thermally stable and display an ionic conductivity within the range 10-4-10-3 S/cm for temperatures between 120 and 160 °C. Moreover, the analysis of the biopolymer's apparent dimensions at nanoscale reveals a dependence of the CNCs' defects, twisting, and aggregation in the presence of the PIL. Preliminary tests using a simple fuel cell setup demonstrate a response of the membranes to the inlet of H2 gas, with a generation of electrical current. These findings provide a solid groundwork for further development and future studies of biopolymer/PIL electrolytes for energy applications. © 2021 The Authors.
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| 4. |
- Hasani, Mohammad, 1985, et al.
(författare)
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Short-Range Order and Transport Properties in Mixtures of the Protic Ionic Liquid [C 2 HIm][TFSI] with Water or Imidazole
- 2020
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-5207 .- 1520-6106. ; 124:9, s. 1767-1777
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the effect of adding different molecular cosolvents, water or imidazole, to the protic ionic liquid 1-ethylimidazolium bis(trifluoromethanesulfonyl)imide, i.e., [C2HIm][TFSI]. We explore how the added cosolvent distributes within the ionic liquid by means of molecular dynamics simulations and X-ray scattering. We also analyze the degree of short-range heterogeneity in the resulting mixtures, finding that while imidazole easily mixes with the protic ionic liquid, water tends to form small clusters in its own water-rich domains. These differences are rationalized by invoking the nature of intermolecular interactions. In aqueous mixtures water-water hydrogen bonds are more likely to form than water-ion hydrogen bonds (water-TFSI bonds being particularly weak), while imidazole can interact with both cations and anions. Hence, the cation-anion association is negligibly influenced by the presence of water, whereas the addition of imidazole creates solvent-separated ion pairs and is thus able to also increase the ionicity. As a consequence of these structural and interactional features, transport properties like self-diffusion and ionic conductivity also show different composition dependencies. While the mobility of both ions and solvent is increased considerably by the addition of water, upon adding imidazole this property changes significantly only for molar fractions of imidazole above 0.6. At these molar fractions, which correspond to a base-excess composition, the imidazole/[C2HIm][TFSI] mixture behaves as a glass-forming liquid with suppressed phase transitions, while homomixtures such as imidazole/[HIm][TFSI] can display a eutectic point.
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| 5. |
- Martinelli, Anna, 1978, et al.
(författare)
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A New Solid-State Proton Conductor: The Salt Hydrate Based on Imidazolium and 12-Tungstophosphate
- 2021
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Ingår i: Journal of the American Chemical Society. - : American Chemical Society (ACS). - 1520-5126 .- 0002-7863. ; 143:34, s. 13895-13907
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Tidskriftsartikel (refereegranskat)abstract
- We report the structure and charge transport properties of a novel solid-state proton conductor obtained by acid-base chemistry via proton transfer from 12-tungstophosphoric acid to imidazole. The resulting material (henceforth named Imid3WP) is a solid salt hydrate that, at room temperature, includes four water molecules per structural unit. To our knowledge, this is the first attempt to tune the properties of a heteropolyacid-based solid-state proton conductor by means of a mixture of water and imidazole, interpolating between water-based and ionic liquid-based proton conductors of high thermal and electrochemical stability. The proton conductivity of Imid3WP·4H2O measured at truly anhydrous conditions reads 0.8 × 10-6 S cm-1 at 322 K, which is higher than the conductivity reported for any other related salt hydrate, despite the lower hydration. In the pseudoanhydrous state, that is, for Imid3WP·2H2O, the proton conductivity is still remarkable and, judging from the low activation energy (Ea = 0.26 eV), attributed to structural diffusion of protons. From complementary X-ray diffraction data, vibrational spectroscopy, and solid-state NMR experiments, the local structure of this salt hydrate was resolved, with imidazolium cations preferably orienting flat on the surface of the tungstophosphate anions, thus achieving a densely packed solid material, and water molecules of hydration that establish extremely strong hydrogen bonds. Computational results confirm these structural details and also evidence that the path of lowest energy for the proton transfer involves primarily imidazole and water molecules, while the proximate Keggin anion contributes with reducing the energy barrier for this particular pathway.
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| 6. |
- Martinelli, Anna, 1978, et al.
(författare)
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Local anisotropy in single crystals of zeotypes with the MFI framework structure evidenced by polarised Raman spectroscopy
- 2020
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Ingår i: Physical Chemistry Chemical Physics. - : Royal Society of Chemistry (RSC). - 1463-9084 .- 1463-9076. ; 22:3, s. 1640-1654
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Tidskriftsartikel (refereegranskat)abstract
- Polarised Raman spectroscopy is used to characterise the local structure in single crystals of zeotypes, namely silicalite-1 and ZSM-5, which share the MFI framework structure. Attributes favourable for applying polarised Raman spectroscopy are the orthogonal axes of these single crystals and their size, i.e. 10 to 30 micrometers in all three directions. We show that the intensity of certain vibrational modes in silicalite-1 depends on the polarisation of the incident light, reflecting the anisotropic character of the molecular bonds contributing to these vibrations. Using these observations, and by estimating the depolarisation ratio (rho) and the pseudo-order factor (f), we propose a more accurate assignment of the Raman active modes. More precisely, Raman intensities peaked at 294, 360, 383 and 472 cm(-1) are attributed to bending modes in 10-, 6-, 5- and 4-membered rings, respectively. In the region of stretching modes, the vibration at 832 cm(-1) is assigned to Si-O-Si bonds shared between 5-membered rings, which have an orientation parallel to the a-axis of the crystal. By virtue of having a strongly polarised character, the modes at 472 and 832 cm(-1) can be used as orientational indicators. The proposed assignment is supported by the good agreement between experimental and simulated polar plots, where Raman intensities are plotted as a function of the polarisation angle of the incident light. Finally, upon partial substitution of Si atoms by Al, the crystalline structure is maintained and almost no spectroscopic changes are observed. The only significant difference is the increased width of most vibrational modes, which is consistent with the local lower symmetry. This is also seen in the angular dependence of selected vibrational modes that compared to the case of pure silicalite-1 appear less polarised. In the Raman spectrum of ZSM-5 a new feature at 974 cm(-1) is observed, which we attribute to Al-OH stretching. In the high frequency range, the O-H stretching modes are observed which arise from the Si-O(H)-Al Bronsted acid sites. The intensity of the characteristic mode at 3611 cm(-1) reveals an anisotropic character as well, which is in line with previous findings from solid state NMR that Al atoms distribute nonrandomly within the MFI framework structure.
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| 7. |
- Mazzapioda, Lucia, et al.
(författare)
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Composite nafion-catio 3-δ membranes as electrolyte component for pem fuel cells
- 2020
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Ingår i: Polymers. - : MDPI AG. - 2073-4360. ; 12:9, s. 1-14
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Tidskriftsartikel (refereegranskat)abstract
- Manufacturing new electrolytes with high ionic conductivity has been a crucial challenge in the development and large-scale distribution of fuel cell devices. In this work, we present two Nafion composite membranes containing a non-stoichiometric calcium titanate perovskite (CaTiO3−δ ) as a filler. These membranes are proposed as a proton exchange electrolyte for Polymer Electrolyte Membrane (PEM) fuel cell devices. More precisely, two different perovskite concentrations of 5 wt% and 10 wt%, with respect to Nafion, are considered. The structural, morphological, and chemical properties of the composite membranes are studied, revealing an inhomogeneous distribution of the filler within the polymer matrix. Direct methanol fuel cell (DMFC) tests, at 110◦ C and 2 M methanol concentration, were also performed. It was observed that the membrane containing 5 wt% of the additive allows the highest cell performance in comparison to the other samples, with a maximum power density of about 70 mW cm−2 at 200 mA cm−2 . Consequently, the ability of the perovskite structure to support proton carriers is here confirmed, suggesting an interesting strategy to obtain successful materials for electrochemical devices.
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| 8. |
- Vavra, Szilvia, 1990, et al.
(författare)
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An imidazolium ionic liquid as effective structure-directing agent for the fabrication of silica thin films with vertically aligned nanochannels
- 2020
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Ingår i: Microporous and Mesoporous Materials. - : Elsevier BV. - 1387-1811. ; In Press
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Tidskriftsartikel (refereegranskat)abstract
- In parallel to the increasing variety of ionic liquids that show different kinds of nanometer-scale structuration in their pure and solved forms, there is a raising interest in exploring the possibility of using ionic liquids as soft-templates for the synthesis of mesoporous materials. We report the case of 1-hexadecyl-3-methylimidazolium chloride (C16MIMCl), a surface active ionic liquid (SAIL), here used as an excellent soft-template for the formation of vertically aligned, uniform mesochannels, with a well defined pore width of 2.5 nm in silica thin films deposited with the electrochemically assisted self-assembly (EASA) method. The obtained mesochannels run through the entire thickness of the films and after removal of the ionic liquid the emptied mesochannels ensure a thorough mass transport to the substrate, here monitored by the redox-active electrochemical probe Ru(II)/Ru(III) during cyclic voltammetry (CV). Moreover, the mechanism of pore formation is explained; unlike the mechanisms reported for short chain imidazolium ionic liquid silica templates, in the case of C16MIMCl the dominating so-called cooperative interaction is the electrostatic attraction between the C16MIM+ and the network-forming negatively charged silicate oligomers. Therefore, this study provides a better understanding of the templating behavior of long chain imidazolium ionic liquids and motivates further research on the synthesis of ionic liquid-based functional hybrid materials.
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| 9. |
- Vavra, Szilvia, 1990, et al.
(författare)
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Transport Properties and Local Structure of an Imidazole/Protic Ionic Liquid Mixture Confined in the Mesopores of Hydrophobic Silica
- 2021
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Ingår i: Journal of Physical Chemistry C. - : American Chemical Society (ACS). - 1932-7447 .- 1932-7455. ; 125:4, s. 2607-2618
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Tidskriftsartikel (refereegranskat)abstract
- The local structure and the molecular dynamics of an imidazole/protic ionic liquid mixture have been investigated while confined in only ca. 5 nm mesopores of silica particles. The walls of the silica pores were functionalized with trioctyl groups to ensure a hydrophobic character, and a series of hybrid materials with varying liquid-to-silica ratios were investigated. Results from vibrational spectroscopy (both Raman and infrared) indicate that the local ion-ion interactions as well as the nature of hydrogen bonds inside the nanopores are not significantly different from the case of the bulk liquid mixture. Nevertheless, the ionic conductivity decreases rapidly and monotonically with decreasing amount of liquid, while the self-diffusion coefficients measured by pulsed field gradient nuclear magnetic resonance (NMR) show a distinct dependence on composition. The population of molecules outside the particles seems to contribute with an enhanced diffusivity, while the molecules inside the mesopores diffuse at a rate comparable to that observed in the bulk liquid. In addition, when experimentally possible, we have measured higher diffusivities for the exchangeable -NH proton than for any other molecular species, which is indicative of a decoupled proton motion. Results from X-ray scattering, employed to elucidate the local molecular structure, reveal an additional feature characteristic of the nanoconfined state, which is associated with a real space distance of about 3.5 nm. This distance describes a specific molecular organization inside the mesopores and may reflect the formation of a monolayer of the octyl-imidazolium cations self-assembled at the hydrophobic silica surface. Such a local structure would favor the localization of charges, including the exchangeable protons. In addition, the analysis of molar conductivity suggests that a major problem with a low pore filling is the emergence of discontinuities throughout the liquid phase.
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