Influences of alkaline treatment on the structure and catalytic performances of ZSM-5/ZSM-11 zeolites with alumina as binder

Influences of alkaline treatment on the structural properties and catalytic performances of ZSM-5/ZSM-11 composite zeolites with alumina as binder at different preparation steps were studied in the present investigation. Temperature-programmed desorption of ammonium (NH3-TPD) and pyridine infrared (Py-IR) spectra revealed that alkaline treatment sequences changed both the distribution and amount of the acidities in the ZSM-5/ZSM-11-Al2O3 samples. The mesopores created by alkaline treatment were found beneficial for the diffusion of aromatic molecules, as determined by the xylene-uptake experiments using a tapered element oscillating microbalance (TEOM). In 1-hexene isomerization and aromatization reactions, the sample after extrusion followed by alkaline treatment exhibited excellent aromatization activity and stability compared with other samples undergoing different treatment sequences. The enhanced catalytic performance could be attributed to the redistribution of acid sites and introduction of more mesopores.