C-13 AND H-1 MAGIC-ANGLE-SPINNING NMR-STUDIES OF THE CONVERSION OF METHANOL OVER OFFRETITE ERIONITE INTERGROWTHS

C-13 and H-1 NMR with magic-angle spinning (MAS) has been used to monitor the conversion of methanol to low-molecular-weight hydrocarbons over intergrowths of the zeolites offretite and erionite with varying contents of the two structures. The sample richest in offretite shows the lowest selectivity to light olefins; this is correlated to the ease of formation of long-chain polymeric hydrocarbons within the intracrystalline space of offretite. The presence of such polymers is confirmed by C-13 MAS NMR and we attribute it to the uninterrupted one-dimensional pore system. In erionite, where the channel system is constricted at every 15.2 angstrom, polymers cannot form. It appears that a degree of channel "tortuosity" is preferable in reactions which produce readily oligomerizable molecules, in order to prevent undesirable side reactions.