A. Philippou et Mw. Anderson, SOLID-STATE NMR INVESTIGATION OF ETHYLBENZENE REACTIONS OVER HMOR ANDPT-HMOR CATALYSTS, Journal of catalysis, 167(1), 1997, pp. 266-272
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.