Effect of multi-step desilication and dealumination treatments on the performance of hierarchical EU-1 zeolite for converting methanol to olefins

Abstract

Multi-steps sequential alkaline and acid treatments were applied on EU-1 zeolite to develop more mesoporosity surface area and to offer more active sites. Different concentrations of NaOH (0.1, 0.25 and 0.5 M) were used to treat parent EU-1 with different cyclic times, followed by a treatment with HNO3 (4 M) also for different cycles. The treated and the parent EU-1 samples were assessed on the conversion of methanol to olefins. The multi-step sequential treatments succeed to create more mesopores as compared with single-step treatment. This improvement was confirmed by BET analysis and NLDFT calculations for pore size distribution. The total acidity was measured using TPD and the quality of the active sites was characterized by in situ FTIR spectroscopy of adsorbed pyridine. Solid state NMR was used to study the position of Al in the EU-1 framework. The main advantage of this multi-step treatment is the preservation of EU-1 crystallinity, which was calculated using XRD. The multi-step treatment yielded an increase in the mesoporosity surface area by 24% and an enhancement of the total acidity, up to five times larger than the parent EU-1 crystals. Furthermore, the selectivity of propylene was increased from 0%, in the case of parent EU-1, to 50% of the product stream together with large enhancement of the stability of methanol conversion and life time.