Measuring sorption effects at zeolite acid sites: pursuing ideas from W.O.Haag

The catalytic activity and selectivity of a Br phi nsted-acid site in a zeo lite is affected not only by the intrinsic strength of the site but also by the environment surrounding the site. Probing the environment, which is la rgely the result of van der Weals attractions and repulsions with the zeoli te cavity in the immediate vicinity of the site, is a challenging problem. This paper will review some recent progress on characterizing the site envi ronment. Calorimetric results for methane adsorption in TON, MTW, and UTD-1 will be reported to demonstrate how strong the effect of pore size can be on the sorption properties. Next, the application of alkylamine temperature -programmed desorption will be discussed for discriminating Br phi nsted si tes in the main channels of FER from those sites that are located inside th e eight-ring side channels. Finally, characterization of the site environme nt using C-13 NMR of adsorbed (CH3COCH3)-C-13 and H-1 NMR of CH3CN will be discussed. For coverages below one per site, it will be shown that NMR dyna mical studies of these molecules in various high-silica zeolites provide im portant information about confinement of the molecule by its environment. ( C) 2000 Elsevier Science B.V. All rights reserved.