Fabrication of highly mesoporous ZSM-48 zeolite by anionic surfactant-organosilane system for catalytic conversion of methanol to gasoline

Abstract

A highly mesoporous ZSM-48 zeolite has been prepared using low-cost anionic surfactant sodium dodecylsulphate (SDS) as mesopore-generating agent and short-chain 3-aminopropyltrimethoxysilane (APTMS) as co-structure directing agent. The mesoporosity formation took place through the interaction between the silica species/APTMS and SDS molecules existing in the gel composition. In the synthesis solution with a pH slightly less than ten, the methoxysilyl moiety in APTMS was hydrolysed to the –SiO3 units and became incorporated inside the zeolite crystals while the positively charged ammonium site of APTMS interacted with the negatively charged head group of the SDS. Aggregation of aluminosilicate/APTMS species around the SDS micelles during the crystallization process, led to the formation of a mesoporous zeolite. In this study, a conventional ZSM-48 and seven ZSM-48 zeolites from different mixtures containing SDS, APTMS and SDS-APTMS with different APTMS/SiO2 molar ratios were synthesized. Changes in the properties of the synthesized samples were investigated by XRD, FTIR, SEM, TEM, nitrogen adsorption/desorption isotherms, NH3-TPD and TGA. The optimum ZSM-48/Sur/0.008OS zeolite prepared with APTMS/SiO2 molar ratio of 0.008 exhibited both bundled needle-like and spherical morphologies. The catalytic conversion of methanol to gasoline (MTG) was evaluated in a fixed-bed reactor, and the results revealed that mesoporosity development using Sur-OS system enhanced catalytic activity of ZSM-48/Sur/0.008OS catalyst compared to the other sample. The optimum zeolite showed long stable phase of 40 h and liquid hydrocarbon yield of 42% was achieved for 100% methanol conversion in 22 h of reaction. The proposed method opens a new and simple route for the synthesis of hierarchically porous ZSM-48 with tunable porosity using low-cost anionic surfactants.