An in situ 13C MAS NMR study of zeolite catalysed alkylation of polar and non-polar aromatics

E. B. Pomakhina, I.I. Ivanova, Y. G. Kolyagin, A.I. Rebrov

Proc. NATO ARW Magnetic Resonance in Colloid and Interface Science, PP-36, St. Petersburg, June 26-30, 2001

ABSTRACT. The 13C MAS NMR study was performed in situ to investigate the mechanisms of aniline and toluene methylation over acidic zeolites. Adsorption of aniline and methanol on zeolite HY leads to strongly adsorbed aniline species, amenable to cross polarization, and three types of methanol species with different mobility: i) mobile "intracrystalline" methanol, ii) species with limited mobility due to interaction with absorbed aniline and iii) small amounts of surface methoxy groups. In the case of toluene and methanol, methanol is more strongly adsorbed than toluene. As a result, no toluene-methanol adsorption complexes are formed and methanol gives only two species: surface methoxy groups and methanol adsorbed on zeolite. Aniline methylation reaction starts at 373 K, while in the presence of toluene, it begins only at 423 K. The main alkylation products are N-methylaniline and o-xylene, respectively. The results show that methoxy species are responsible for N-alkylation but not for C-alkylation. This conclusion is confirmed by the experiments on the interaction of aniline and toluene with methoxylated zeolite HY. In the case of toluene methylation, methanol adsorbed species are the precursors for alkylation.

Laboratory of Kinetics and Catalysis