# Furfural Hydrogenation on Modified Niobia
## 3 Results
### Catalysts Characterisation
Undoped Nb\({}_{2}\)O\({}_{5}\) displays a broad Raman feature centred at 706 cm\({}^{-1}\), that can be assigned to symmetric stretching modes of Nb-O in distorted octahedra (Figure 4B, spectrum (_a_) [43]. Interestingly, the incorporation of a second element gives rise to frequency shifts to: (i) higher frequencies, like in the case of W-containing Nb\({}_{2}\)O\({}_{5}\) (719 cm\({}^{-1}\)) (Figure 4B, spectra (_b_); (ii) lower frequencies, for Ti-containing catalyst (694 cm\({}^{-1}\)) (Figure 4B, spectrum _c_). The shift can be explained in terms of the specific weight of the dopant elements, i.e., heavier species (like W\({}^{6+}\)) will shift the bands to higher frequencies, while lighter dopants (like Ti\({}^{4+}\)) would shift the bands to lower frequencies. In addition, doped supports show broader Raman signals, due to a higher disordered degree (as observed in XRD patterns) [44]. In turn, signals corresponding to TiO\({}_{2}\) and WO\({}_{3}\) oxides were always absent in the supports. All these observations suggest either an effective interaction of the promoter with Nb\({}_{2}\)O\({}_{5}\), or the incorporation of the dopants in framework positions. Figure 4: X-ray diffraction (XRD) patterns (**A**) and Raman Spectra (**B**) of Nb\({}_{2}\)O\({}_{5}\)-based supports: (a) Nb\({}_{2}\)O\({}_{5}\); (b) W-Nb\({}_{2}\)O\({}_{5}\); (c) Ti-Nb\({}_{2}\)O\({}_{5}\). BET analyses were carried out on the pure supports in order to evaluate differences in surface area (Table 2). Upon inclusion of W to the niobia lattice, the surface area increased from 95 to 130 m\({}^{2}\cdot\)g\({}^{-1}\) (Nb\({}_{2}\)O\({}_{5}\) and W-Nb\({}_{2}\)O\({}_{5}\) respectively). On the other hand, the addition of Ti had the opposite effect and the surface area decreased to 35 m\({}^{2}\cdot\)g\({}^{-1}\). The adsorption of basic probe molecules followed by IR analysis is a common technique used to investigate the surface acidity of solid catalysts. Here IR analysis of adsorbed pyridine (Py) has been performed. As reported in the literature, the contact with the amine gives rite to several bands in the range of 1400-1700 cm\({}^{-1}\), depending on the type of the interaction between pyridine and catalyst surface (physisorbed pyridine, Lewis acid sites, Bronsted acid sites). A weak interaction between the catalyst and the probe molecule, resulting from very weak or no acidity (physisorption or hydrogen bonding), gives rise to an adsorption band in the range of 1440-1450 cm\({}^{-1}\) and another one at 1580-1600 cm\({}^{-1}\). These bands easily decrease with the temperature and over 100 \({}^{\circ}\)C physisorbed pyridine could be considered fully desorbed. When pyridine is interacting with Lewis acid site, two main absorption peaks are detected: one centered at ca. 1450 cm\({}^{-1}\) (v\({}_{19\text{b}}\) mode) and a second centered at ca. 1610 cm\({}^{-1}\) (v\({}_{8\text{a}}\) mode). In the case of Lewis acidity also a small band at 1580 cm\({}^{-1}\) could be observed. On the other hand, in presence of Bronsted acid sites, a proton transfer occurs to form the pyridinuim ion though the protonation of pyridine. This results in a band at 1550 cm\({}^{-1}\) (v\({}_{19\text{b}}\) mode), followed by a band near 1640 cm\({}^{-1}\) (v\({}_{8\text{a}}\) mode). Also a band at ca. 1490 cm\({}^{-1}\) is usually detected, but it was not unambiguously assigned to a specific acid site, being identified as the result of either kind of interactions. Importantly, pyridine on both Lewis and Bronsted sites is resistant to outgassing with bands that could be detected also at high temperature [45; 46; 47]. In Figure 5 we reported the FT-IR spectra of pyridine recorded after degassing at 150 \({}^{\circ}\)C for the investigated materials. All the catalysts exhibit the bands pattern typical for Lewis acids sites, with the bands at 1448 cm\({}^{-1}\) and 1609 cm\({}^{-1}\) (and the small one at 1576 cm\({}^{-1}\)), whereas Bronsted sites are absent.