Surface species formed during aniline methylation on zeolite H-Y investigated by in situ MAS NMR spectroscopy

Aniline alkylation with methanol on zeolite H-Y has been studied using in s itu C-13 MAS NMR spectroscopy under batch conditions. To clarify the main r eaction pathways, the conversion of methanol as well as the interaction of aniline with surface methoxy groups were investigated under similar conditi ons. Methanol-C-13 and methyl iodide-C-13 were used as labeled reactants. C o-adsorption of aniline and methanol-C-13 on zeolite H-Y led to strongly ad sorbed aniline molecules, assigned to aniline H-bonded to zeolite Bronsted acid sites, and three types of methanol species of different mobility: mobi le methanol molecules with a liquid-like characteristics and two types of r igid methanol species with solid-like characteristics attributed to a metha nol adsorption complex with aniline and surface methoxy groups, respectivel y. Among all the methanol species observed, only surface methoxy groups wer e shown to be responsible for aniline alkylation which takes place at tempe ratures from 373 to 523 K. The formation of surface methoxy groups was foun d to be a limiting step of the overall reaction. The primary alkylation pro duct is N-methylaniline. Toluidines and N-methyltoluidines are formed at te mperatures from 523 to 623 K after complete conversion of methanol to N-met hylaniline. Therefore, isomerization or disproportionation of N-methylanili ne was proposed to account for their formation. (C) 2001 Academic Press.