Copyright © 2014 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Editor: Michael Rowan; Editorial Board Chairs: Uwe Bornscheuer, Luis A. Oro, Bert Weckhuysen
Impact Factor: 5.044
ISI Journal Citation Reports © Ranking: 2013: 26/136 (Chemistry Physical)
Online ISSN: 1867-3899
Cover Picture: (ChemCatChem 5/2012)
Qualification and Quantification of Reduced Sites Quantification of spin concentration by electron paramagnetic resonance (EPR) is a complicated issue, in particular if overlapping contributions of different paramagnetic centers exist. This problem can be overcome by using high-frequency EPR, by which contributions with different g values can be disentangled. This approach is similar to the use of ever increasing magnetic fields in NMR spectroscopy. Double integration of the EPR spectrum results in step-like features, familiar to those seen in NMR spectroscopy, which permits a direct readout of relative spin concentrations. Invoking an external or internal spin standard like Mn2+, it is also possible to determine the absolute spin concentration. This method was applied for the qualification and quantification of reduced sites on supported vanadium oxide catalysts used for sample reactions, such as the oxidative dehydrogenation of propane or deep reduction with propane or hydrogen. The data show the important influence of the support material on the type of potentially active sites and the degree of reduction obtained.