# Furfural Hydrogenation on Modified Niobia
## 3 Results  
### Catalysts Characterisation  
SEM-EDX analyses were performed on the metal-doped niobia supports (Figure 2) in order to calculate the effective loading of the dopant into the niobia structure. The two supports show similar dopant loading very close to the nominal value of 10 at% (Table 1). Pt have been deposited onto the niobium oxide-based supports by MVS following the procedure previously used for other kind of supports [35; 37; 38]. TEM micrographs collected on the three samples (Figure 3) revealed the niobium oxide-based supports densely populated by monodispersed Pt nanoparticles with very small particle sizes, ranging mainly 1.0-1.5 nm, regardless of the support used. \begin{table}
\begin{tabular}{c c} \hline \hline
**Support** & **Dopant [at\%]** \\ \hline Ti-Nb\({}_{2}\)O\({}_{5}\) & 9.68 \\ W-Nb\({}_{2}\)O\({}_{5}\) & 9.35 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Dopant loading on the niobia based supports by Energy-Dispersive X-ray Spectroscopy. Figure 2: Representative scanning electron microscopy (SEM) images of (**A**) Ti-Nb\({}_{2}\)O\({}_{5}\) and (**B**) W-Nb\({}_{2}\)O\({}_{3}\). Figure 4 depicts XRD patterns of niobia-based supports. All the materials only show two well-defined diffraction maxima at 20 values of ca. 23 and 46\({}^{\circ}\) (Figure 4A). Those signals can be ascribed to 001 and 002 planes in any ReO\({}_{3}\)-type related structure, and are assigned to a well-ordered vertex-sharing octahedra along one direction, showing an opposite vertex distance of ca. 3.8 A [39; 40]. The rest of the observed signals show a broad profile, indicating the amorphous nature of the \(ab\)-plane of the structure in all cases. Accordingly, it becomes difficult to ascribe the distribution of the atoms along \(a\) and \(b\) directions to a specific polymorph. Nevertheless, we can estimate the partial substitution of the  
of Nb by the dopants by analyzing the shifts in 20 of the abovementioned 001 signal. Analyzed _c_-parameter values, calculated from 20 values of 001 signal by using Bragg equation are summarized in Table 2. It can be seen that the incorporation of Ti\({}^{4+}\) into Nb\({}_{2}\)O\({}_{5}\) framework leads to a decrease in the _c_-parameter, from 3.89 A to 3.80 A, which is in line with ionic radius of Nb\({}^{5+}\) and Ti\({}^{4+}\) (0.64 and 0.60 A, respectively) [41]. On the other hand, when W\({}^{6+/5+}\) is used as promoters, _c_-parameter slightly increases up to 3.90 A (Table 2). When dealing with these pseudocrystalline materials (i.e., with a well-ordered structure just along one crystallographic direction), the demonstration of the partial substitution of Nb by XRD is not so direct. In this sense, the variation of cell parameters can present opposite trends, i.e., the isomorphic substitution in the crystal framework can derive in an increase of the dimensions of the unit cell in some specific directions, while showing decreasing trends in others. This has been observed in the partial substitution of W for Mo in tetragonal tungsten bronze-based materials [42]. HR-TEM analysis on Pt nanoparticles dispersed on the niobia-based oxides (Figure S1) confirmed the presence of a pseudocrystalline phase of the supports. All of them appeared to be constituted by primary nano-domains, 7-20 nm long and 4-10 nm in width stacked on each other, mainly along their length, to form agglomerates. According to the XRD results, the direction of elongation of the domains was found to be coincident with the [001] direction, coincident with the c-axis of the lattice. In order to shed some light on this issue, we have analyzed Nb\({}_{2}\)O\({}_{5}\)-based supports by Raman spectroscopy (Figure 4B). In this case, the incorporation of W\({}^{6+/5+}\) or Ti\({}^{4+}\) within Nb\({}_{2}\)O\({}_{5}\) framework should promote variations on the nature of metal-oxygen bonds with respect to the undoped material.