The use of electron paramagnetic resonance (EPR) for the investigation of catalytic surfaces by means of adsorbed nitroxides is discussed. The possibilities of the paramagnetic probe method in terms of qualitative and quantitative control of the acidity of the catalyst surfaces is demonstrated. Models of the acid site structures in accordance with EPR data are presented.
E. V. Lunina, "EPR Spectroscopy of Adsorbed Nitroxides to Investigate Catalyst Surfaces," Appl. Spectrosc. 50, 1413-1420 (1996)