Novel extruded fixed-bed MTO catalysts with high olefin selectivity and high resistance against coke deactivation Original Research Article

This report describes the catalytic performances of AlPO4/ZSM-5 extrudates in comparison to conventional alumina- and silica-bound extrudates in the fixed-bed MTO (methanol to olefins) conversion. The novel AlPO4/ZSM-5 extrudates are produced with an aluminium phosphate binder which undergoes a phase transition into an AlPO4-tridymite phase upon calcination of the greenbodies. The finished AlPO4/ZSM-5 extrudates are macroporous and mechanically very stable. In contrast to alumina, this novel matrix does not exhibit catalytic self-activity, and it does not release aluminium which is incorporated in the zeolite lattice. At temperatures above 400 °C, AlPO4/ZSM-5 extrudates show superior activity, propylene selectivity and stability. The coke deactivation of AlPO4/ZSM-5 extrudates can further be reduced dramatically, if a pre-reactor is installed upstream, where an equilibrium mixture of dimethyl ether (DME), methanol and water (XMeOH = 87.7% at 275 °C) is produced. In contrast, the insertion of the DME pre-reactor has no significant effect on the coke resistance when extrudates with alumina- or silica-matrices are used.