Size, Shape, and Site Selectivities in the Photochemical Reactions of Molecules Adsorbed on Pentasil Zeolites Effects of Coadsorbed Water

摘要

The photochemistry of methylbenzyl benzyl ketones (ACOB) in the presence of pentasil zeolites follows strikingly different pathways due to the location of the absorbed ketone. The product distribution, in terms of the cage effect (efficiency of geminate radical combination), demonstrates the effects of sorption and diffusion on the radical species produced by photolysis. p-ACOB is readily adsorbed within the pentasil framework and produces p-AB as the primary product. In contrast, the photolysis product distributions of o-ACOB can be dramatically varied depending upon the extent of its adsorption into the framework. By addition of a nonreactive titrant, such as water, after the ketone adsorption, the photolysis product distributions can be systematically varied depending upon the aluminum content of the framework. The observed results are completely described by considerations of (a) the size and shape sorption of the pentasil zeolites, (b) the sorption of water by the hydrophilic sites of the pentasil zeolites (which depend upon the framework aluminum content), and (c) the hydrophobic characteristics of pentasil channels which do not contain framework aluminum.