Design principles of operando ultraviolet-visible and electron paramagnetic resonance spectroscopy setups for active site characterization in ion-exchanged zeolites
Open access
Autor(in)
Alle anzeigen
Datum
2024-03-01Typ
- Journal Article
ETH Bibliographie
yes
Altmetrics
Abstract
Cu- and Fe-exchanged zeolites have been widely investigated for their applicability in selective partial oxidation of CH4 and abatement of environmentally harmful nitrogen oxides. However, the differentiation between spectator and active sites is cumbersome due to their dynamic co-existence, which aggravates the elucidation of the redox dynamics of the latter. Therefore, correlated multi-spectroscopic approaches carried out under operando conditions are needed in order to disentangle the inherent reactivity of specific species. Here we describe the conceptualization of complementary operando spectroscopic methods for the investigation of ion-exchanged zeolites employed in redox reactions. The potential and versatility of this approach are demonstrated by means of two exemplary case studies. First, we present the insight generated by two custom operando ultraviolet-visible and electron paramagnetic resonance spectroscopy setups operating in batch mode into CH4-to-CH3OH conversion over Cu-exchanged mordenite. In addition to recording the method-dependent spectroscopic fingerprints of distinct Cu centers, the overall CH4 consumption is simultaneously monitored in both setups. The extracted apparent activation energies of the reactive centers obtained from the two systems are in good agreement with each other allowing to link the bulk reactivity to the intrinsic site-specific kinetics of all Cu centers. Second, the EPR setup is equipped with a flow reactor designed to carry out modulated excitation experiments with phase-sensitive detection in order to improve the signal-to-noise ratio and time resolution. The cell is employed to study the conversion of NO via selective catalytic reduction over Fe-exchanged ferrierite. In combination with operando X-ray absorption spectroscopy, a small portion of active Fe species consisting of monomers in gamma-positions and oligomeric structures located in the main channel is identified, which are kept in a redox active state under relevant reaction conditions and thus sustain the chemical transformation of NO. Mehr anzeigen
Persistenter Link
https://doi.org/10.3929/ethz-b-000657569Publikationsstatus
publishedExterne Links
Zeitschrift / Serie
Catalysis TodayBand
Seiten / Artikelnummer
Verlag
ElsevierThema
Heterogeneous catalysis; Zeolites; Operando spectroscopy; Electron paramagnetic resonance spectroscopy; UV-Visible spectroscopy; Modulated excitation spectroscopyOrganisationseinheit
03746 - Van Bokhoven, Jeroen A. / Van Bokhoven, Jeroen A.
03810 - Jeschke, Gunnar / Jeschke, Gunnar
Förderung
ETH-48 20-1 - Time-resolved in situ EPR spectroscopy for heterogeneous catalysis (ETHZ)
ETH Bibliographie
yes
Altmetrics