## 3 Results and Discussion
### Characterization
The acidic sites in the zeolites, which are more relevant in structures with a low Si/Al ratio, may act as anchoring sites for the migrated species [32; 33]. In this way, the higher reduction of micropore surface area for ZSM-5(15) might be explained. Regarding ITQ-2 samples, the two raw zeolites present considerable differences in the S\({}_{\text{BET}}\) values and, especially, in external surface area. These results indicate that the delamination is greater for ITQ-2(\(\infty\)), being coherent with the fact that a decreasing Al content favors the delamination process [34]. H\({}_{2}\)-TPR was performed to study the reduction behavior of the supported NiO particles. The results show that the incorporated Ni is reduced in the range 200-550 \({}^{\circ}\)C (Figure 2). In the case of the catalysts supported on ITQ-2, the profiles seem to be formed by broader components suggesting a greater heterogeneity regarding size of NiO nanoparticles and interaction with the support. Ni in the form of NiO located in the external surface of the zeolite is reported to be reduced between 330 and 385 \({}^{\circ}\)C [15; 20], while Ni interacting in a higher degree with ITQ-2 can be reduced at 400 \({}^{\circ}\)C [35]. As it can be seen, the component at higher temperatures dominates the profiles of these samples. This finding supports that a higher Ni dispersion is obtained when it is dispersed on delaminated ITQ-2, as it was already indicated by XRD results. Nevertheless, the larger level of reducibility of the nickel catalyst supported on ITQ-2 (15) compared to the pure silica ITQ-2 (41% and 54%, respectively) seems to indicate that the nickel interaction with the support would be slightly higher for the pure silica ITQ-2 zeolite, explaining the lower size of the NiO nanoparticles detected in this sample. For the catalysts supported on ZSM-5, Ni reduction takes place within a similar range of temperatures. However, for these samples, the contribution at lower temperatures is predominant. This peak has been attributed to the reduction of bulk NiO, while the one at higher temperatures is related to smaller NiO nanoparticles or NiO inside the zeolite pores [36; 37]. To evaluate the Bronsted acidity of these samples, pyridine adsorption at different temperatures was followed by FTIR. The amount of adsorbed pyridine in the catalyst was calculated from the area of the band at 1545 cm\({}^{-1}\), which is assigned to Bronsted acidity [28]. The results can be seen in Table 2. These tests revealed that the sample supported on pure silica ITQ-2 shows no Bronsted acidity, as expected due to the absence of Al in this material. Its counterpart (ITQ-2(15)) presents a slightly higher acid character. ZSM-5 samples follow a similar trend, that is, the sample with higher Al content shows a higher Bronsted acidity. However, in this case the difference was broader than in the case of ITQ-2 samples. The increase of Bronsted acidity with Al content is in good agreement with previous results [38; 39]. Figure 2: H\({}_{2}\)-TPR profiles of the 5 wt.% Ni catalysts supported on ITQ-2 and ZSM-5 with different Si/Al ratios. In previous studies, it is pointed out that Bronsted acidity is related to the hydrophobicity of the material. In general, for a given zeolite type, materials with lower Bronsted acidity also presents a higher hydrophobic character [40; 41]. This hydrophobicity character might be relevant in this particular reaction, as water is one of the reaction products. HR-TEM was performed to examine Ni\({}^{0}\) particle sizes in the reduced catalysts (Figure 3). A narrow particle size distribution was obtained for the catalyst 5 Ni/ITQ-2(\(\infty\)) with a very small mean particle size (2.4 nm). The rest of the samples show a wider particle size distribution with bigger Ni\({}^{0}\) particles, especially for ZSM-5 supported catalysts for which sizes between 5 and 40 nm were found.