Insight into the Mechanisms of the Ethylbenzene Disproportionation: Transition State Shape Selectivity on Zeolites

Abstract

The direct experimental evidence shows that ethylbenzene disproportionation is a transition state shape selective reaction on zeolites: a bimolecular reaction mechanism via diphenylethane-mediated pathway on large-pore zeolites X and Y (ca. 0.74 nm) and a monomolecular reaction mechanism on medium-pore zeolites ZSM-5 (ca. 0.56 nm) via the ethoxy-mediated intermolecular ethyl group transfer. The lifetime of bulky diphenylethane species was prolonged by a fine-tune of FAU-zeolites, which makes this transition state detectable by 13C MAS NMR spectroscopy. Due to tunable catalytic properties and pore shapes, zeolites are promising catalysts toward emulating the efficiency and selectivity in desired reactions.

Solid-state nuclear magnetic resonance investigations of the nature, property, and activity of acid sites on solid catalysts

“…There are two reaction pathways under discussion: (i) The bimolecular diphenylethane-mediated reaction pathway (Scheme 5) and (ii) the monomolecular ethyltransfer reaction pathway (Scheme 6) [178,179]. Recent in situ 13 C MAS NMR studies gave experimental evidence for these two mechanistic pathways on acidic large-pore and medium-pore zeolites affected by the transition state shape selectivity during the acid-catalyzed ethylbenzene disproportionation on zeolites [179,180]. These studies were performed under batch conditions using catalyst samples activated and loaded with the reactants inside of glass inserts, which were sealed and stepwise heated after finishing the preparation.…”

Utilisation de matériaux à base d’argiles modifiées dans la conversion du toluène

“…Selon la litté rature [8,16,[18][19][20], la ré action de dismutation du toluè ne peut avoir lieu selon deux mé canismes possibles montré s par la Fig. 3.…”

Room‐Temperature Alkane Reactivity in Zeolites: An H/D Exchange Study

“…[3,4] On the basis of the initial product distribution at high temperature, the Haag-Dessau mechanism [5,6] (s bond protolysis as in superacids [7][8][9] ) is generally suggested as the first alkane activation step, but hydride abstraction, oxidation, and alkene impurities have also been evoked to account for the formation of the cationic intermediate. [10][11][12] Simple carbenium ions are generally considered as transient species (unless they have a large charge delocalization) within the zeolite channels and that the most stable intermediates are the framework-bound alkoxy species. [13][14][15] The existence of carbenium ions as short-lived reaction intermediates in equilibrium with the alkoxy species is supported by the Koch reaction, the halogen switch reaction, [16][17][18] single-event microkinetics, [19] and theoretical calculations.…”