###### Abstract
Regarding the zeolites, medium pore structures with pore dimensions close to the dynamic diameter of benzene, the desired product [23], are the most selective [26; 27]. Among the 10-ring zeolites, ZSM-5 [28; 29; 30; 31] and MCM-22 [30; 32; 33; 34; 35; 36; 37; 38] have been thoroughly studied and are the most efficient in terms of benzene yield and catalyst life. However, other medium pore zeolites have also been reported as active for MDA, such as IM-5 [39; 40; 41] or TNU-9 [42; 41]. Regarding the reaction mechanism and the active sites involved, it is widely accepted that methane is first activated on the Mo sites and that the reaction intermediates formed will further oligomerize, cyclate and dehydrogenase on the Bronsted acid sites [34; 43; 44; 45; 46; 47; 48; 49]. In the last few decades, a large effort has been made trying to identify the active species, as well as their formation and how these are affected by the physical-chemical properties of the zeolite used as support [50; 51; 52; 53; 54; 55; 56]. Moreover, according to the literature, the incorporation procedure of the molybdenum into the zeolitic material can have an important impact on the physico-chemical properties of the final Mo/zeolite catalyst [49; 57]. Although different procedures have been described to prepare the Mo/ZSM-5 catalysts, the most employed technique for Mo incorporation is the incipient wetness using ammonium heptamolybdate (AHM) as the metal precursor [43]. The large [Mo\({}_{7}\)O\({}_{24}\)\({}^{6-}\)] anions are located mainly on the external surface of the zeolite [58], and the MoO\({}_{3}\) crystals are formed by calcination at temperatures in the range of 623 to 773 K. [PERSON] et al. [50; 55; 59] proposed the preparation of the Mo/ZSM-5 catalyst by solid state ion-exchange, by physically mixing molybdenum trioxide with the zeolite followed by a calcination step that will force the migration of the Mo species from the external surface into the zeolite micropores. The cationic Mo species, anchored to the zeolite framework, have been identified as the active sites responsible for the selective conversion of methane into aromatics, whereas the presence of Mo clusters at the external surface of the zeolite has been related to the formation of coke [49]. Although a proper dispersion degree and location of the Mo-oxo species has been shown to be key for an optimum methane conversion and benzene selectivity, the active sites are not the starting oxides, but the Mo-oxo-carbide species formed by reduction of the former by the methane feed in the first stage of the MDA process [47; 60; 61]. Thus,the reducibility of the starting Mo-oxo species, directly related to their size and location, will play a determinant role. Regarding the contribution of the Bronsted acid sites (BAS), they are known to promote the dispersion of the metal species into the zeolite micropores [62]. Although not essential for dehydroromatization, as evidenced by [PERSON] [63], the BAS also enhance the conversion of the intermediates formed on the Mo-species into the desired aromatics [59; 64; 65]. Recent studies propose the contribution of a hydrocarbon pool mechanism to the MDA reaction [46; 47; 48; 66; 67], similar to the one described for the methanol-to-hydrocarbon (MTH) process. In the present work, we have studied the influence of the different preparation steps on the physico-chemical properties of the final Mo/ZSM-5 catalyst and, consequently, on their catalytic performance for the MDA reaction. The same parent ZSM-5 zeolite and Mo content (6 wt. %) have been used in all cases, so that the location and dispersion of the metal will only depend on the preparation procedure. Thus, on the one hand two Mo incorporation methodologies have been compared, incipient wetness (IW) and solid-state reaction (SSR). On the other, these two samples have been calcined in a muffle, under a static air atmosphere (SC--static calcination) or in a fixed bed reactor under air flow (DC--dynamic calcination).