Conversion of methanol over 10-ring zeolites with differing volumes at channel intersections: comparison of TNU-9, IM-5, ZSM-11 and ZSM-5.

Four 3D 10-ring zeolites, IM-5, TNU-9, ZSM-11 and ZSM-5, with Si/Al = 14-24 and crystal sizes below 2 microns, were tested as catalysts for the methanol to hydrocarbons reaction (MTH) at atmospheric pressure, 350 °C and WHSV = 9 h(-1). All catalysts gave initially full methanol conversion, and showed strikingly similar effluent product selectivities. However, their life-time duration differed significantly, and decreased in the order: ZSM-11 > ZSM-5 ≫ TNU-9 > IM-5. A main difference between the two groups of stability behaviour was the size of cavities formed by channel intersections; larger cavities in TNU-9 and IM-5 leading to polyaromatics formation and a more rapid deactivation compared to ZSM-5 and ZSM-11. Effluent yield-conversion plots suggested that polymethylated benzene intermediates were more important in IM-5 and TNU-9 than in ZSM-5 and ZSM-11, where alkene methylation and cracking reactions seemed to dominate product formation. However, this difference had only minor influence on effluent selectivity.