Abstract
The Lewis and Bronsted acid properties of SnBEA zeolites as well as SnO2 supported on silica BEA have been examined by means of IR spectroscopy of adsorbed pyridine, 2,6-ditertbutylpyridine, and deuterated acetonitrile. Three types of surface sites have been detected and assigned to (i) framework Sn centers possessing Lewis acid properties; (ii) weak Bronsted acid sites associated with framework tin atoms; and (iii) nonframework SnO2 particles which possess Lewis acidity. The total amount of Lewis sites can be determined using pyridine as a probe molecule, while the type of Lewis sites can be distinguished by FTIR of adsorbed acetonitrile. The band at 2316 cm–1 is attributed to strong framework sites, whereas the band at 2287 cm–1 is attributed to nonframework sites. Bronsted acid sites can be characterized using 2,6-ditertbutylpyridine (bands at 3363, 1613, and 1530 cm–1) and deuterated acetonitrile (band at 2308 cm–1). The relative amount of Lewis and Bronsted acid sites on SnBEA can be varied by treatm...
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