Direct synthesis of [B,H]ZSM-5 by a solid-phase method: AlF siting and catalytic performance in the MTP reaction

Abstract

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 Al_F 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 Al_F 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.