Recent applications of electron magnetic resonance (EMR) techniques in heterogeneous catalysis

A kilowatt pulsed 94 GHz electron paramagnetic resonance spectrometer with high concentration sensitivity, high instantaneous bandwidth, and low dead time

“…Higher frequencies offer better spectral resolution, concentration and absolute sensitivity, orientation selectivity, lower cavity dead time, higher conversion factors, and access to a higher energy scale that can simplify problems associated with high energy zero-field transitions or reduce ͑or enhance͒ effects due to forbidden transitions. The past 20 years have seen a huge increase in interest in high field EPR ͑HFEPR͒ as can be seen from both general reviews of the field, 1 special editions on HFEPR, 2 and the large number of specialist reviews available, including those on inorganic systems, 3 spin labeling, 4 photosynthesis, 5 dynamics of biomecules, 6 instrumental techniques, 7,8 quasioptical techniques, 9 transition metal ion complexes and metalloproteins, 10 instrumentation and bioinorganic systems, 11 integer spin systems, 12 molecular magnetic clusters, 13 catalysis, 14 ferromagnetic and antiferromagnetic systems, 15 relaxation, 16 and swept frequency techniques. 17 However, it is the parallel exploitation of a wide variety of pulse techniques that is revolutionizing the field ͑see the well known text by Schweiger and Jeschke 18 for an excellent review͒.…”

Monitoring transition metal ions (TMI) in oxide catalysts during (re)action: the power of operando EPR

“…Electron paramagnetic resonance (EPR) is a unique tool for analyzing structural and electronic peculiarities of paramagnetic TMI [1][2][3][4][5][6][7][8][9] since it provides simultaneous information on valence state, coordination geometry and electronic interactions of TMI between each other and with reactant molecules and with the support. While the valence state of TMI determines the total spin which must be different from zero for EPR detection, differences in the coordination geometry are sensitively reflected by intrinsic interactions of the electron spin with the orbital momentum (g-tensor), as well as with the spin of the nucleus (A-tensor) and, if present, with other electrons in the same atom (D-tensor).…”