## 3 Results and Discussions
### Characterization Results
Indeed, not only the impregnation method but also the calcination mode altered the H\({}_{2}\)-TPR profile of the Mo/ZSM-5 samples (see Figure 3). According to the literature [52; 75; 76], four regions can be distinguished based on the Mo reduction temperature, a low temperature region in the range of 473-650 K (I) related to the partial reduction of amorphous polymeric molybdate species, a second region (II, 650-875 K) ascribed to the reduction of MoO\({}_{3}\) to MoO\({}_{2}\), a third one (III, 875-1173 K) assigned to the reduction of MoO\({}_{2}\) to MoO, and a high temperature region (IV, T \(>\) 1173 K) related to the reducibility of the [Mo\({}_{2}\)O\({}_{3}\)]\({}^{+2}\) species occluded inside the zeolitic channels, which are more difficult to be reduced. The main differences among the four catalysts are related to the reduction profiles in regions II and III. Thus, MoZ5-IW-SC presents two peaks in region II at 700 and 760 K, assigned to the reduction of MoO\({}_{3}\) particles on the external surface, easily reducible, and within the zeolite pores, to MoO\({}_{2}\). A lower H\({}_{2}\) consumption in region III suggests that not all the Mo\({}^{4+}\) species formed and observed in region II are susceptible to further reduction. Sample MoZ5-SSR-DC presents a very similar profile, although the peak maximums are slightly shifted to lower temperatures. However, sample MoZ5-SSR-SC, prepared by solid-state reaction but calcined in a muffle, presents the region II and region III peaks shifted to higher temperatures and in different proportions as those observed for MoZ5-IW-DC. These higher reduction temperatures of sample MoZ5-SSR-SC could be related to the presence of large MoO\({}_{3}\) species, as observed by FESEM (see Figure 2), more difficult to be reduced than small MoO\({}_{3}\) particles, highly dispersed on the zeolite surface. However, once this first reduction occurs, a larger peak is observed in Region III indicating a higher H\({}_{2}\) consumption, which could be attributed to a dispersion of the large Mo agglomerates under the H\({}_{2}\)-TPR conditions (H\({}_{2}\) flow and increasing temperature) facilitating the reduction of these new Mo species formed. The reduction in size of the Mo particles on the MoZ5-SSR-SC sample after H\({}_{2}\)-TPR measurement was confirmed by SEM (see Figure S3 in the Supplementary Materials), indicating that, indeed, exposure of the sample to the measurement conditions led to a dispersion of the Mo species. The fourth sample, MoZ5-IW-DC, prepared by incipient wetness and calcined in air flow, presents two peaks with similar intensities in regions II and III, suggesting that all the MoO\({}_{3}\) species that are first reduced to MoO\({}_{2}\) are further reduced in a second step. Moreover, the region II peak is more symmetric and shifted towards higher temperature as compared to the profile obtained for the IW sample calcined in a muffle, suggesting a more homogenous speciation of the Mo sites and an enhanced migration of the Mo species into the zeolite micropores. All catalysts present analogous reduction bands in regions I and IV, but the intensity of the region IV peaks varies depending on the calcination procedure, and the samples calcined in air flow (DC) present higher hydrogen consumption at high temperature indicating that a larger proportion of Mo species have migrated inside of the zeolitic channels during the calcination step. If exposure to a H\({}_{2}\) flow during the H\({}_{2}\)-TPR measurement resulted in an increased dispersion of the Mo species for catalyst MoZ5-SSR-SC, a similar improvement could be expected for the other catalyst prepared by solid ion exchange, MoZ5-SSR-DC. Thus, the two SSR samples were treated by controlled temperature increase from Tr to 973 K under N\({}_{2}\) flow and cooled down for characterization and testing.