Journal of Catalysis 246 (2007) 35–39 www.elsevier.com/locate/jcat The effect of support morphology on the activity of HZSM-5-supported molybdenum catalysts for the aromatization of methane Alper Sarıo ˘ glan a,1 , Ömer Tunç Sava¸ sçı b , Ay¸ se Erdem- ¸ Senatalar c,∗ , Alain Tuel a , Gilbert Sapaly a , Younès Ben Taârit a a Institut des Recherches sur la Catalyse, C.N.R.S., 69626, Vileurbanne cedex, France b Materials and Chemical Technologies Research Institute, TUBITAK Marmara Research Center, P.K. 21, 41470 Gebze/Kocaeli, Turkey c Department of Chemical Engineering, ˙ Istanbul Technical University, Maslak, 34469 ˙ Istanbul, Turkey Received 27 June 2006; revised 3 October 2006; accepted 4 October 2006 Available online 19 December 2006 Abstract The aromatization of methane was investigated over Mo 2 C supported on several HZSM-5 zeolites with different morphologies and Si/Al ratios. X-ray diffraction, elemental analyses, X-ray photoelectron spectroscopy, 27 Al NMR spectroscopy, nitrogen adsorption, and scanning electron microscopy were used to characterize the supports. Support morphology was observed to play a crucial role in this reaction, which was studied under conditions in which actual rates could be compared. Although rates did not vary linearly either with the total number of the acid sites or with the external surface area, turnover frequencies of the surface acid sites, calculated using the Si/Al ratios determined from XPS measurements, were observed to vary linearly with the external surface area.  2006 Published by Elsevier Inc. Keywords: Aromatization; Methane; Molybdenum; Si/Al ratio; Morphology; External surface 1. Introduction Conversion of methane into useful chemicals has been and still is a subject of renewed efforts worldwide. Several routes have been explored over the previous two decades. In addition to methane conversion into syngas, which is of real industrial significance, more ambitious routes, such as direct conversion into oxygenates [1–4], methanation of olefins [5], oxidative coupling of methane [6–9], and conversion of methane into ben- zene and hydrogen, have been explored [10–29]. The latest developments were concerned with the latter reaction carried out in the presence of various transition- metal oxide-loaded inorganic carriers. Mainly molybdenum- and rhenium-based active components deposited over HZSM-5 were thoroughly investigated [22–29]. * Corresponding author. Fax: +90 212 285 2925. E-mail address: aerdem@itu.edu.tr (A. Erdem- ¸ Senatalar). 1 Present address: Energy Institute, TUBITAK Marmara Research Center, P.K. 21, 41470 Gebze/Kocaeli, Turkey. In the case of molybdenum-based catalysts, the activation procedure was scrutinized, and whatever the nature of the pre- cursor, molybdenum was converted, in the presence of methane, under the reaction conditions, into molybdenum carbide [12,13, 24]. Quite recently, Derouane and colleagues showed that it is possible to synthesize bulk or supported metastable fcc molyb- denum carbide with a formula MoC 1−x . HZSM-5-supported fcc carbide exhibited higher activity and stability and selectiv- ity to benzene in the dehydrocyclization of methane than the hexagonal β -Mo 2 C [30–32]. As far as the reaction was concerned, it proceeded via the formation of C 2 H 2 (or C 2 H 4 ) over the molybdenum carbide species, acting both as dehydrogenating and coupling functions to create the first C–C bond, and further cyclization and aroma- tization occurring on the support acid sites. In addition to ben- zene, a number of aromatics, including xylene, divinylbenzene, and naphthalene, were produced after successive alkylation of benzene by the C 2 intermediate. Higher aromatics and carbon issued from the simple decomposition of methane to its ele- ments escaped direct analysis, although a number of studies 0021-9517/$ – see front matter  2006 Published by Elsevier Inc. doi:10.1016/j.jcat.2006.10.005