Comparative investigation of the MTH induction reaction over HZSM-5 and HSAPO-34 catalysts

Abstract

Methanol to hydrocarbons (MTH) induction reaction was comparatively investigated over HZSM-5 and HSAPO-34 catalysts combined with on line thermogravimetry analysis of catalyst weight increment by intelligent gravimetric analyzer (IGA) studies. The influence of catalyst topology and acidity and reaction temperature on the reaction performance were correlated with the confined organics formation and evolution over the catalysts. For the latter stage of the MTH induction period, methanol conversion over HZSM-5 catalyst was proved a well-defined autocatalysis process, while over HSAPO-34, the increasing rate of methanol conversion was retarded due to accumulation of methyladamantanes. There existed a similar deactivation behaviour for HZSM-5 catalysts with low Si/Al ratios and HSAPO-34 catalysts during the temperature-programmed MTH (TP-MTH) reaction. But the IGA studies showed that the change of the retained species amount was quite different: for TP-MTH reaction over HZSM-5, the amount firstly increased and then decreased to a stable value; while for HSAPO-34, the amount kept increasing until reached a constant value. MTH induction reaction over HZSM-5 catalyst with different Si/Al ratios and HSAPO-34 catalysts with different Si contents were also investigated. All these findings revealed the influence of catalyst topologies on the formation of retained species and then on the catalyst activity during the MTH induction reaction.