Seed-assisted synthesis of ZSM-23 zeolites in the absence of alkali metal ions

The seed-assisted synthesis of ZSM-23 zeolite in the absence of alkali metal ions (denoted as SNNa) was investigated. Highly crystallized SNNa with needle-shape morphology and size of 500-1100 nm in length and 50-200 nm in diameter can be synthesized. Much attention was paid to the roles of alkali metal ions during the crystallization process. The absence of Na+ can effectively avoid the impurity quartz formation and promote SNNa crystallization in a broad range of SiO2/Al2O3 ratio between 80 and 200, whereas the crystallization rate was slowed down at the same time. On the contrary, the presence of Na+ had a significant effect both on the nucleation and crystal growth processes. The bifunctional catalyst Pt/H-SNNa prepared, showed good catalytic performance in the hydroisomerization of n-hexadecane due to its small crystal size, appropriate acidity and acid site distribution. (C) 2017 Elsevier Inc. All rights reserved.