Organotemplate-free syntheses of ZSM-34 zeolite and its heteroatom-substituted analogues with good catalytic performance

The organotemplate-free route for syntheses of aluminosilicate ZSM-34 zeolite and its heteroatom-substituted analogues (B, Ga, and Fe) in the presence of zeolite L seeds solution has been extensively investigated. Many factors such as the amount of zeolite L seeds solution, SiO₂/Na₂O ratio in the starting aluminosilicate gel, crystallization temperature, and time influence the crystallization of ZSM-34 zeolite significantly. The pure phase of ZSM-34 zeolite could only be obtained in a narrow phase diagram of Na ₂O-Al₂O₃-SiO₂-H₂O by a comprehensive consideration of these factors. Heteroatoms such as B, Ga, and Fe substituted ZSM-34 zeolites can also be synthesized by this organotemplate-free route. Catalytic tests in the conversion of methanol to olefins (MTO) at the temperature of 400 °C and weight hourly space velocity (WHSV) of 0.5 h ^-1 over aluminosilicate ZSM-34 and its analogues containing framework B and Ga show that these ZSM-34 catalysts exhibit higher selectivities for ethylene and propylene (>80%) than ZSM-5 zeolite (<55%), which is reasonably attributed to the shape selectivity of ZSM-34 with smaller pore size of (5.2 Å) than ZSM-5 (5.6 Å).