Zeolite ZSM-5 is nowadays widely used as a catalyst, especially in the petroleum refining and petrochemical industries. As a matter of experience, zeolite ZSM-5 can be synthesized in good quality with n(Si)/n(Al) ratios ranging from ca 12 to infinity. For certain catalytic applications, it is of considerable interest to synthesize ZSM-5 zeolites with an n(Si)/n(Al) ratio lower than 12.