Facile moderate-temperature hydrothermal design of nanocrystalline coffin-shaped ZSM-5 catalyst for transformation of CH3OH to C2H4/C3H6

Abstract

Different crystallization times were studied during hydrothermally synthesis of ZSM-5 framework at moderate temperature to investigate the physicochemical properties and MTO catalytic behavior. The ZSM-5 samples were synthesized at moderate temperature (250 °C) and different crystallization times (24, 18, 12, 6, and 3 h). The synthesized samples were analyzed by XRD, FESEM, EDX, BET-BJH, FTIR, and TPD-NH3 experimental approaches. The results revealed that the purity of crystalline phase, nucleation rate, crystallinity, morphology, porosity, and acidic properties of catalysts depended on the condition of moderate temperature synthesis with strong dependence on crystallization time. This was indicative of the ZSM-5 zeolite prepared at short crystallization time (3 h) facilitated facile design of coffin-shaped ZSM-5 particles which were capable of producing improved properties could provide some useful indication for MTO reaction. So, the MTO catalytic process was carried out using the specific MTO reaction condition of T = 460 °C, CH3OH: H2O = 1:1 (vol:vol) and the feed gas hourly space velocity (GHSV) = 10500 cm3/gcat.h). The ZSM-5(250-3) catalyst showed an enhanced selectivity toward desired olefins, whereas it presented 65% selectivity to propylene and 9% selectivity to ethylene after 35 h on stream. The possible reaction pathway for facile design synthesis of ZSM-5 catalyst via moderate temperature was proposed.