Quaternary Ammonium Surfactant Assisted Synthesis of Hierarchical Porous Hβ Zeolite for Aniline Catalytic Condensation

Hierarchical porous Hβ zeolites (H-Hβ) were synthesized by a quaternary ammonium surfactant assisted method and characterized by XRD, XRF, SEM, TEM, N₂ adsorption-desorption and NH₃-TPD. Catalytic performance of the H-Hβ zeolites for aniline condensation to product diphenylamine was evaluated in a fixed bed reactor. The results show that mesoporosity is successfully introduced into the H-Hβ zeolites by adding quaternary ammonium surfactant to form a micro- and mesoporous composite structure, which remarkably enlarges the pore volume and diameter of the H-Hβ zeolites and promote molecule diffusion. Longer carbon chains of quaternary ammonium surfactants are in favor of forming larger pore volume and diameter of H-Hβ zeolites. Compared with conventional Hβ zeolites (aniline conversion rate of 18.5%), H-Hβ zeolites can significantly increase aniline conversion to 31.0%~33.23% and keep the selectivity of diphenylamine over 96%. In addition, with the decrease of SiO₂/Al₂O₃ ratio, the acid amount of H-Hβ-16 zeolites increases gradually. The increased acid amount in H-Hβ-16 zeolites improves aniline conversion while the selectivity of diphenylamine remains unchanged.