Novel aluminophosphate (AlPO) bound ZSM-5 extrudates with improved catalytic properties for methanol to propylene (MTP) reaction

Abstract

Novel aluminophosphate (AlPO) binders consisting of dense phases of alpha-cristobalite and tridymite were prepared by the treatment of pseudo-boehmite (AlO(OH)) with phosphoric acid. The ZSM-5 extrudates prepared by using AlPO binders have been characterized by XRD, N 2 sorption, NH 3-TPD, 27Al and 31P NMR techniques to elucidate the changes that occurred in the textural properties of the catalyst and their implications on the catalytic activity of the resultant ZSM-5-based extrudates towards methanol to propylene (MTP) reaction. XRD indicated the chemical interaction of P with the alumina binder to form a highly dense crystalline phase of aluminophosphate, alpha-cristobalite. N 2 adsorption, while NH 3-TPD studies revealed the changes in pore morphology of AlO(OH) binder and acidity of ZSM-5 in phosphorus containing extrudates. The drastic decrease in mesoporosity of the AlO(OH) observed after phosphorus addition indeed envisions the disappearance of inter-crystalline voids in the AlO(OH), probably due to a change in its morphology from the crystalline phase to amorphous AlPO phase. 27Al and 31P NMR studies further confirmed the formation of AlPO in these samples. The resultant ZSM-5-based extrudates exhibited enhanced properties of hydrothermal stability, mechanical strength, propylene yield and coke resistance in methanol to propylene (MTP) reaction. The positive aspect of P addition was continuously increased with P amount; at optimum P/Al (binder) ratio of ∼0.8, the catalyst exhibited about 80% yield to C 2–C 4 olefins with the major component being propylene (∼50%) at near 100% methanol conversion. The catalyst also exhibited the stable performance in the studied period of 150 h.