SOLID-STATE NMR INVESTIGATION OF ETHYLBENZENE REACTIONS OVER HMOR ANDPT-HMOR CATALYSTS

Ethylbenzene reactions on HMOR and Pt-HMOR have been studied by means of solid-state MAS NMR. These experimental findings clearly indicate t hat disproportionation via the intermediacy of diphenylethane structur e constitutes the first steps of this catalytic process over both HMOR and Pt-HMOR. In addition, ethylbenzene is suggested to undergo nonbra nching rearrangements via the intermediacy of a two-electron-three-cen ter bond leading to a C-13-label transfer from alpha- to beta-position of the side chain. This appears to be a major catalytic event over bo th catalysts. At later stages, disproportionation of ethylbenzene via dealkylation/alkylation steps accompanied by secondary reactions of et hylene proceeds freely on HMOR, whereas it is very much suppressed on Pt-HMOR. While dealkylation is very pronounced over Pt-HMOR, alkylatio n is very much limited by rapid hydrogenation of ethylene to ethane on Pt sites. Based on the spectroscopic evidence of this investigation, a number of schematic representations are illustrated to address the m echanistic approaches taken in this contribution. (C) 1997 Academic Pr ess.