In this comprehensive review, recent progress and developments on perfluorinated sulfonic-acid (PFSA) membranes have been summarized on many key topics. Although quite well investigated for decades, PFSA ionomers’ complex behavior, along with their key role in many emerging technologies, have presented significant scientific challenges but also helped create a unique cross-disciplinary research field to overcome such challenges. Research and progress on PFSAs, especially when considered with their applications, are at the forefront of bridging electrochemistry and polymer (physics), which have also opened up development of state-of-the-art in situ characterization techniques as well as multiphysics computation models. Topics reviewed stem from correlating the various physical (e.g., mechanical) and transport properties with morphology and structure across time and length scales. In addition, topics of recent interest such as structure/transport correlations and modeling, composite PFSA membranes, degradat...

New Insights into Perfluorinated Sulfonic-Acid Ionomers

The utilization of solar energy for the conversion of CO2 into valuable organic products is one of the best solutions to solve the problems of global warming and energy shortage. The development of photocatalysts capable of reducing CO2 under visible light, especially those containing earth-abundant metals, is significant. Herein we report that a series of earth-abundant Fe-containing MOFs (MIL-101(Fe), MIL-53(Fe), MIL-88B(Fe)) show photocatalytic activity for CO2 reduction to give formate under visible light irradiation. The direct excitation of the Fe–O clusters in these MOFs induces the electron transfer from O2– to Fe3+ to form Fe2+, which is responsible for the photocatalytic CO2 reduction. Among the three investigated Fe-based MOFs, MIL-101(Fe) showed the best activity due to the existence of the coordination unsaturated Fe sites in its structure. All three amine-functionalized Fe-containing MOFs (NH2-MIL-101(Fe), NH2-MIL-53(Fe) and NH2-MIL-88B(Fe)) showed enhanced photocatalytic activity in compari...

Fe-Based MOFs for Photocatalytic CO2 Reduction: Role of Coordination Unsaturated Sites and Dual Excitation Pathways

The characteristics of pre-edge peaks in K-edge x-ray absorption near edge structure (XANES) spectra of 3d transition metals were reviewed from viewpoints of the selection rule, coordination number, number of d-electrons, and symmetry of the coordination sphere. The contribution of the electric dipole and quadrupole transition to the peaks was discussed on the basis of the group theory, polarized spectra, and theoretical calculations. The pre-edge peak intensity for Td symmetry is larger than those for Oh symmetry for all 3d elements. The intense pre-edge peak for tetrahedral species of 3d transition metals is not due to 1s–3d transition, but transition to the p component in d–p hybridized orbital. The mixing of metal 4p orbitals with the 3d orbitals depends strongly on the coordination symmetry, and the possibility is predictable by group theory. The transition of 1s electron to d orbitals is electric quadrupole component in any of the symmetries. The d–p hybridization does not occur with regular octahedral symmetry, and the weak pre-edge peak consists of 1s–3d electric quadrupole transition. The pre-edge peak intensity for a compound with a tetrahedral center changes as a function of the number of 3d electrons regardless of the kind of element; it is maximized at d0 and gradually decreases to zero at d10. The features of pre-edge peaks in K-edge XANES spectra for 4d elements and the L1-edge for 5d elements are analogous with those for 3d elements, but the pre-edge peak is broadened due to the wide natural width of the core level. Copyright © 2008 John Wiley & Sons, Ltd.

Assignment of pre‐edge peaks in K‐edge x‐ray absorption spectra of 3d transition metal compounds: electric dipole or quadrupole?

(Article begins on next page) Anyone can freely access the full text of works made available as \"Open Access\". Works made available under a Creative Commons license can be used according to the terms and conditions of said license. Use of all other works requires consent of the right holder (author or publisher) if not exempted from copyright protection by the applicable law. Availability: This is the author's manuscript

/pdf/reactivity-of-surface-species-in-heterogeneous-catalysts-1vtf7rqr9y.pdf

Reactivity of Surface Species in Heterogeneous Catalysts Probed by In Situ X-ray Absorption Techniques

Iron copper zeolite (Fe-Cu-ZSM-5) with aqueous hydrogen peroxide is active for the selective oxidation of methane to methanol. Iron is involved in the activation of the carbon–hydrogen bond, while copper allows methanol to form as the major product. The catalyst is stable, re-usable and activates methane giving >90 % methanol selectivity and 10 % conversion in a closed catalytic cycle (see scheme).

Direct Catalytic Conversion of Methane to Methanol in an Aqueous Medium by using Copper‐Promoted Fe‐ZSM‐5

Structure and reactivity of framework and extraframework iron in Fe-silicalite as investigated by spectroscopic and physicochemical methods

The interaction of pyridine with acidic H-ZSM5, H-β, and H-MORD zeolites and a perfluorosulfonic superacidic membrane (H-Nafion) has allowed us to study the IR spectrum of PyH+ hydrogen bonded to the negative zeolite skeleton (Z-) or to CF2SO3- groups of the membrane. In the presence of excess Py the formation of PyH+···Py is also detected. On H-MORD (a zeolite with higher Al content) the adsorption of Py at room temperature is limited to the external surfaces of the crystallite, owing to the blockage of channel mouths caused by the PyH+ formed in high concentration. The IR spectra of hydrogen-bonded PyH+ in the ν(NH···) stretching region are strongly influenced by Fermi resonance effects with the overtones and combinations of low-frequency modes. In the H-Nafion/Py system the modification induced by the proton transfer on the internal modes of the −SO3H groups (with formation of SO3- species) gives additional information on the proton transfer process. To complete the assignment of all the observed surfa...

Interaction of Pyridine with Acidic (H-ZSM5, H-β, H-MORD Zeolites) and Superacidic (H-Nafion Membrane) Systems: An IR Investigation

When molecules of low-medium proton affinity (B = N2, CO, C2H4, C2H2, propene, methylacetylene, acetonitrile and H2O) are adsorbed on acidic zeolites, the resulting host-guest interactions in the cavities and in the channels are dominated by hydrogen bonding in neutral Z-H…B adducts between the Bronsted groups Z-bH (Z = zeolite framework) and the base. If the interaction is sufficiently strong and the protonated products stable (ethylene, acetylene, propene and methylacetylene) the hydrogen bonded precursors are slowly consumed with formation of olygomeric products entrapped into the zeolite cavities. Acetonitrile gives a stronger hydrogen bonding interaction not followed by protonation. Water initially gives neutral complexes; however when more than one water molecule per protonic site is present, H5O2+·nH2O species are formed. When molecules of high proton affinities are adsorbed (NH3 and Py), B-H+···Z− ionic pairs readily appear. The modifications induced on the spectrum of B-H+ by interaction with Z− can be used to probe the basicity of the negatively charged framework. At higher filling conditions B-H+···B dimers are also observed. The basic IR spectroscopy of all these hydrogen bonded systems is discussed in detail.

Host- guest interactions in zeolite cavities

Summary The object of this study is the interaction of HZSM-5 with probe molcules, characterized by different basicity by using IR spectroscopy. The formation of H-bonded species and the proton transfer are considered. Experimental results are compared with literature data (experimental and theoretical)

R. Buzzoni

Papers

Structure and reactivity of framework and extraframework iron in Fe-silicalite as investigated by spectroscopic and physicochemical methods

Interaction of Pyridine with Acidic (H-ZSM5, H-β, H-MORD Zeolites) and Superacidic (H-Nafion Membrane) Systems: An IR Investigation

Host- guest interactions in zeolite cavities

Interaction of CO2, H2O, CH3OH, (CH3)2O, CH3N, H2S, (CH3)2CO, NH3 and Py with Bronsted acid sites of H-ZSM-5: Comparison of the IR manifestation