2. Experimental
2.1. Catalyst preparation
Na-ZSM-5 zeolites with Si/Al atomic ratio of x (x = 23, 51, 62,
and 107) were hydrothermally synthesized. Tetrapropylammonium
bromide was used as a templating agent. Water glass and
aluminum sulfate were used as silicon and aluminum sources,
respectively. The Si/Al ratio was adjusted by changing the amount
of aluminum sulfate. The starting gel was put in the autoclave
at 433K for 2 days. The obtained products were washed with
ion-exchanged water and calcined at 823K for 8 h in air. The asprepared
Na-ZSM-5 zeolites were ion-exchanged with an aqueous
solution of 0.1 mol L−1 ammonium nitrate in static condition at
343K for 3 days and washed with ion-exchanged water to obtain
their NH4
+ forms. They were transformed into H-ZSM-5 by calcining
at 823K for 8 h in the air.