Whereas the hegemony of the Fischer-Tropsch synthesis is well established for the valorization of methane in the case of important gas fields, the methane dehydro-aromatization reaction remains an interesting solution to convert methane obtained as by-product of oil extraction and thus fight against flaring and global warming. Until now, it was generally accepted that the molybdenum is anchored on the Bronsted acid sites of the zeolite as (Mo2O5)(2+) species. The molybdenum performs the dehydrogenation and coupling of CH4 to ethylene which is consecutively oligomerized to benzene over the Bronsted acid sites. In the present work, we bring evidence that this picture is actually more complicated than it seems. The Si/Al ratio of the zeolite, and consequently the density of available Bronsted acid sites, plays a dramatic role on the anchoring mode of the molybdenum and on its catalytic activity. (c) 2007 Elsevier B.V. All rights reserved.