Zeolite L

A method for the dehydrocyclization and/or isomerization of aliphatic hydrocarbons comprising contacting said hydrocarbons at a temperature in the range of from about 370.degree. C. to about 600.degree. C. with a catalyst so as to convert at least part of the aliphatic hydrocarbons into aromatic hydrocarbons wherein said catalyst comprises a catalytically active metal and zeolite L comprising cylindrical crystallites having basal planes shaped such that the ratio of axial length of curved cylindrical surface (m) to the overall axial length of the crystallite (h) is greater than 0.9, the aspect ratio of (m) to the mean diameter (d) is at least 0.5 and the mean diameter (d) is in the range of at least 0.05 to 0.5 microns, wherein said zeolite is crystallized from a synthesis mixture containing a source of alkali metal selected from the group consisting of potassium and a mixture of potassium and sodium and further containing a source of additional metal selected from the group consisting of magnesium, calcium, barium, manganese, chromium, cobalt, nickel and zinc cations, said additional metal being present in an amount in the range of from about 0.1 ppm to about 0.1 wt % based on said synthesis mixture.