Abstract: Binderless zeolite L particles are prepared by a method in which particles are formed from silica and from 0 to 95 wt % preformed zeolite L crystallites, and the particles are thereafter reacted with an alkaline solution comprising a source of alumina to convert the silica binder to zeolite L. These particles may comprise cylindrical zeolite L crystallites with a mean diameter of at least 0.05 micron in a zeolite L matrix and may be used as catalyst. Also acyclic hydrocarbons are dehydrocyclized and/or isomerized by contacting them at a temperature of from 370.degree. C. to 600.degree. C. with this catalyst incorporating at least one Group VIII metal having dehydrogenating activity to convert at least part of the acyclic hydrocarbons into aromatic hydrocarbons.