C-13 CPMAS NUCLEAR-MAGNETIC-RESONANCE STUDY OF THE ADSORPTION OF 2-PHENETHYLAMINE ON CLAYS

2-Phenethylamine C-13-enriched in the beta position was adsorbed on fo ur different aluminum-exchanged clays: hectorite, Barasym, Laponite RD , and lithium taeniolite. The sites for adsorption were characterized by C-13 high-resolution cross-polarization magic angle spinning nuclea r magnetic resonance (CPMAS-NMR) spectroscopy. Using differences in ch emical shift values and linewidths, three different types of bound amm onium compounds and a motionally restricted bound compound were identi fied. Correlation with charge effects indicated that one of the clay s ites was extremely acidic. The important catalytic sites for the diffe rent clays, the edge or platelet face, interlamellar and some combinat ion of both, were probed by using the trimethylsilyl group as a clay-b locking agent. Silylation of aluminum-exchanged Laponite RD and Li tae niolite had little effect on amine adsorption. This indicates that, fo r these clays, amine adsorption occurred mainly at interlamellar sites . For hectorite, amine adsorption occurred at both surface and interla mellar sites, and silylation had the effect of reducing surface adsorp tion. Silylation of Barasym resulted in a very interesting shift of ad sorption from one kind of surface site to a more acidic surface site.