## 3 Results and Discussions
### Catalytic Results  
In the former section, we have evidenced the impact of the Mo incorporation method on the physico-chemical properties of the final Mo/ZSM-5 catalyst and how the use of an additional pretreatment under N\({}_{2}\) flow can reduce the size of the larger MoO\({}_{3}\) particles and favor the formation and/or migration of cationic Mo species into the zeolite micropores. As a direct consequence of their different textural and acidic properties and of the reactivity of their Mo species, the catalysts are expected to differ also in their catalytic performance. Before starting with the catalytic discussion, however, we would like to note that the catalysts have been activated increasing temperature in methane atmosphere (CH\({}_{4}\):N\({}_{2}\) = 80:20 in vol.%). In this way, the MoC\({}_{x}\)O\({}_{y}\) active species, responsible for the activation of the methane molecules [43, 77] are formed before the reaction temperature (973K) is reached. As described in Section 2.3, this stage is followed by 30 min in N\({}_{2}\) flow before starting to feed the methane mixture. The purpose of this pre-treatment is to have a fully active catalyst, with molybdenum oxo-carbides species already formed, when starting the MDA reaction, and to avoid the competition of both processes [41]. Methane conversion and the hydrocarbon yields versus time on stream (TOS) for the four catalysts obtained by IW and SSR and calcined in air under static (SC) or dynamic conditions (DC) are shown in Figure 4. The initial methane conversion obtained in all cases is around 13%, close to the equilibrium conversion determined by means of Aspen Hysys(r) v.8.0 for a temperature of 973 K using the Gibbs free energy minimization approach, and in good agreement with the values given in the literature [24, 41, 78]. Figure 4: Methane conversion (**A**), total yield to hydrocarbons products (**B**), yield to aliphatic hydrocarbons (**C**), to aromatic hydrocarbons (**D**), to benzene (**E**) and to naphthalene (**F**) versus TOS for catalysts MoZ5-SSR-SC (**a**), MoZ5-SSR-DC (**m**), MoZ5-IW-SC (Definitions/applsci-1225460-i002.pdf), and MoZ5-IW-DC (**e**), at 973 K, atmospheric pressure and w/F = 16 g-h/mol. Despite the comparable initial conversion, the two catalysts obtained by calcination under static conditions, MoZ5-IW-SC and MoZ5-SSR-SC, present a higher deactivation rate and a significantly lower yield to hydrocarbons (see Figure 4A,B, respectively) as compared to the catalysts calcined in N\({}_{2}\) flow (DC). This lower yield to hydrocarbons results from an important reduction of the aromatics and, in particular, of the benzene production (see Figure 4D,E). Moreover, the catalyst obtained by solid ion exchange and calcined in the muffle (MoZ5-SSR-SC) presents the highest coke yields (see Figure 5), as could be expected from the presence of large MoO\({}_{3}\) crystals on the external surface of the zeolites, which, according to the literature [49], are responsible for the formation of coke. On the other hand, the two catalysts obtained by calcination under N\({}_{2}\) flow after Mo incorporation, MoZ5-IW-DC and MoZ5-SSR-DC, present higher yields to aromatics, slightly higher for the latter at short times on stream. This better performance could be related to the improved dispersion of the Mo species and the larger proportion of Mo within the channels, as evidenced by the H\({}_{2}\) consumption in region IV observed by H\({}_{2}\)-TPR. According to the results presented in the former section, the Mo/ZSM-5 samples prepared by solid state reactions were improved in terms of Mo dispersion after N\({}_{2}\) pretreatment, with their properties becoming more similar to those presented by the samples prepared by IW impregnation. The activity of the N\({}_{2}\)-pretreated SSR catalysts is similar to those of the non-pretreated samples (see Figure 6), but the total yield to hydrocarbons is significantly increased in both cases due to an important increase in the production of benzene.