Surface Raman and resonance Raman spectroscopy: Applications in catalysis

Lasar Raman spectroscopy is a valuable technique for performing in situ studies of functioning catalysts. Raman spectroscopy has several important advantages over infrared spectroscopy: opaque samples may be examined, water is a poor Raman scatterer, and low frequency data may be obtained easily. In addition, elevated temperature and pressure studies may be performed using relatively simple sample cell designs. A wide variety of catalysts have been characterized using conventional laser Raman spectroscopy, including silicas, aluminas, zeolites, molybdates, tungstates, chromates, and vanadates. Studies of adsorbed species have involved several probe molecules with pyridine being the most extensively used. Resonance Raman spectroscopy offers enormous advantages in studying catalysts because of the very large increase in signal intensity. In addition, the technique may be used to selectively enhance portions of the Raman spectrum. The interaction of several metallo-porphyrins with various supports has been studied with resonance Raman spectroscopy, and the relation to metal deactivation of surfaces will be discussed.