Synthesis and characterization of core-shell Beta/MCM-22 micro-microporous composite zeolites

With Beta zeolite as the core crystals, core-shell Beta/MCM-22 composite zeolites with uniform morphology were synthesized by a two-step hydrothermal method. The composite zeolites were characterized by XRD, SEM, TEM, N₂-adsorption and FT-IR. The results showed the composite zeolites exhibit uniform structured morphology; Beta and MCM-22 zeolites act as core and shell, respectively. The pore structure of Beta/MCM-22 composite zeolites was between those of MCM-22 and Beta zeolites. The amounts of medium acidic sites and brnsted acidic sites are increased markedly (C_B/C_L = 13.80) in the composite zeolites. The surface energy, Si-OH groups and surficial positive charges of Beta zeolites are enriched through Ar-H₂ plasma surface treatment, which contributes to the formation of uniform core-shell Beta/MCM-22 composite zeolites.