It is known to catalytically crack non-aromatic gasoline boiling range hydrocarbons, particularly hydrocarbons such as paraffins and olefins, to lower olefins (such as ethylene and propylene) and aromatic hydrocarbons (such as benzene, toluene and xylenes) in the presence of catalysts which contain a zeolite (such as ZSM-5), as is described in an article by N. Y. Chen et al. in Industrial & Engine