The synthesis of H[Fe,Al]ZSM-5 zeolites with uniform nanocrystals for dimethyl ether to gasoline reaction

Abstract

The conversion of dimethyl ether to gasoline (DTG) over acidic zeolite catalysts is an important non-petroleum route to obtain transportation fuels due to the current shortage of crude oil resources. Here, the H[Fe,Al]ZSM-5 zeolites with uniform nanocrystals were prepared using hydrothermal method and tested for DTG reaction, and the effects of crystallization time on the physicochemical properties of prepared zeolites were investigated by multiple characterization techniques, such as UV–Vis, 27Al MAS NMR, XPS, XRD, FT-IR, ICP-AES, SEM, N2 adsorption–desorption, NH3-TPD and Py-IR. The results indicated that the nanocrystalline H[Fe,Al]ZSM-5 zeolites with high crystallinity could be synthesized in the time of as short as 4 h, and Fe species in zeolite framework mainly exist in the form of isolated Fe3+ in tetrahedral and octahedral coordination. The nanocrystalline H[Fe,Al]ZSM-5 zeolites with crystallization time of 14–48 h had the close and higher acid strength and amounts. The DTG reaction results indicated that the H[Fe,Al]ZSM-5 catalyst with crystallization time of 24 h exhibited the best catalytic performance due to its maximum amount of acid and higher B/L ratio, the DME conversion remained at 100% for about 125 h, and the gasoline yield and the isoparaffin selectivity reached up to 77% and 35.5%, respectively. While the selectivity of aromatics, durene and benzene could be controlled to a low level of about 40%, 2.1% and 0.45%, respectively. The obtained gasoline meets the standard of GB 17930-2011, which could be directly used as the transportation fuel.