Direct synthesis of [B,H]ZSM-5 by a solid-phase method: AlF siting and catalytic performance in the MTP reaction†
Isomorphous boron-substituted HZSM-5 ([B,H]ZSM-5) zeolite was directly synthesized by a solid-phase method, and its properties were characterized by XRD, FE-SEM, N2 adsorption/desorption, FT-IR, ICP-AES, NH3-TPD, py-FTIR, TG, GC-MS, solid MAS-NMR, and UV-vis of Co2+. It was found that the acid distribution was tuned, and the AlF siting was changed when boron was introduced into the ZSM-5 framework, which significantly affected the catalytic performance of BHZ samples in the MTP reaction. The preferential occupation of boron atoms in the channel intersections and sinusoidal channels caused AlF to be sited in the straight and sinusoidal channels, which simultaneously tuned acid distribution and weakened the acid strength in the channel intersections. These changes tuned the dual-cycle mechanism of the MTP reaction, resulting in a lower carbon deposition rate and longer lifetime for BHZ samples, especially for 2.5-BHZ, by comparison with HZ samples.