Development of hierarchical EU-1 zeolite by sequential alkaline and acid treatments for selective dimethyl ether to propylene (DTP)

Developing mesoporosity on the surface of the one-dimensional zeolite provides stronger impact as compared with three-dimensional zeolites because the 1D pore zeolites suffers from diffusion limitation. Recently, we worked to create mesopores on EU-1 (EUO) by alkaline treatment, which yielded significant decrease in micropore volume and the total surface area. The decrease of microporosity corresponded with blockage of active acid sites due to the deposition of many Al species on the pore mouth of zeolites. In this work, desilicated EU-1 samples treated with different NaOH concentrations were again treated with different concentrations of HNO₃ to remove the deposited Al species. The effects of NaOH and HNO₃ concentrations on the crystallinity, morphology, Si/Al ratio, surface area, pore size distribution and acidity of EU-1 were investigated. The samples characterized by XRD, EDX, SEM, BET and NH₃-TPD. The optimum condition for sequential alkaline-acid treatment was obtained with 0.5 M of NaOH followed by 4 M of HNO₃ solution. The mesoporosity increased by 15% for EU-1 the aforementioned sample as compared with the parent zeolite. The total acidity also increased from 0.27 to 0.52 mmol/g. The hierarchical EU-1 samples were evaluated on the conversion of dimethyl ether to olefins. The conversion increased from 37% to 48% together with the increased selectivity of propylene from 11% to 24%, when the parent EU-1 was replaced by the optimized hierarchical EU-1.