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Continuous wave EPR spectroscopy at 35 GHz is an essential cornerstone in multi-frequency EPR studies and crucial for differentiating multiple species in complex systems due to the improved g tensor resolution compared to lower microwave frequencies. Especially for unstable and highly sensitive paramagnetic centers the reliability of the measurements can be improved by the use of a single sample for EPR experiments at all frequencies. Besides the advantages, the lack of common availability of oversized-sample resonators at 35 GHz often limits scientists to lower frequencies or smaller sample geometries, the latter may be non-trivial for sensitive materials. In this work, we present the design and performance of an oversized-sample 35 GHz EPR resonator with a high loaded Q value up to 3300 well suited for continuous wave EPR and single microwave frequency experiments with low excitation power. The design is driven by electromagnetic field simulations and the microwave characteristics of manufactured prototypes were found in agreement with the predictions. The resonator is based on a cylindrical cavity with a TE011 mode allowing for 3 mm sample access. Design targets met comprise high sensitivity, robustness, ease of manufacturing and maintenance. The resonator is compatible with commercial EPR spectrometers and cryostats, allowing for measurements at temperatures down to at least 4 K. To highlight the general applicability, the resonator was tested on metal centers as well as on organic radicals featuring extremely narrow lines. [ABSTRACT FROM AUTHOR]

Identification and quantification of redox‐active centers at relevant conditions for catalysis is pivotal to understand reaction mechanisms and requires development of advanced operando methods. Herein, we demonstrate operando EPR spectroscopy as an important technique to quantify the oxidation state of representative CrPO4 and EuOCl catalysts during propane oxychlorination, an attractive route for propylene production. In particular, we show that the space‐time‐yield of C3H6 correlates with the amount of Cr2+ and Eu2+ ions generated over the catalysts during reaction. These results provide a powerful strategy to gather quantitative understanding of selective alkane oxidation, which could potentially be extrapolated to other functionalization approaches and operating conditions. [ABSTRACT FROM AUTHOR]