# Furfural Hydrogenation on Modified Niobia
## 3 Results
### Catalytic Results  
Depending on the reaction conditions and the catalysts used, the hydrogenation of furfural can proceed in different directions: products of carbonyl hydrogenation, ring hydrogenation, ring opening, etherification, hydrodeoxygenation, and decarboxylation have been reported in literature (Figure 1). Furfural hydrogenation reactions were carried out in this study at 50 \({}^{\circ}\)C and 5 bar of H\({}_{2}\), using ethanol as solvent. Typically, under this mild reaction conditions, furfuryl alcohol (FA) and tetrahydrofurfuryl alcohol (THFA) are reported to be the main products, as a result of the hydrogenation of the carbonyl group and the furan ring (Figure 1). Figure 6 shows the reaction profile of the furfural hydrogenation reaction carried out using Pt/Nb\({}_{2}\)O\({}_{5}\) as catalyst. After 15 min, almost half of the starting substrate was converted (42%) and the main products were furfural diethyl acetal (FEA) and FA (44 and 43% of selectivity respectively), with low amount of THFA being produced as well (7%). The presence of the acetal is not surprising, since it is often reported when the reaction is carried out with solid acid catalysts in low-chain alcoholic solvents (i.e., ethanol). Furfural was fully converted after 1 h and both FA and FEA were transformed. The FA reached a maximum after 30 min of reaction (52%) and then decreased, with a consequent increase of THFA (31% of selectivity after 2 h), whereas FEA decreased over time, with no trace of acetal remained after 2 h. Interestingly, products of hydrogenolysis (ring-opening and hydrodeoxygenation) such as 1,2-pentanediol (1,2-PDO), 1,5-pentanediol (1,5-PDO), and1-pentanol (POH) were present in significant amounts in the final reaction mixture. In particular, 1,2-PDO and 1,5-PDO (9 and 13% of selectivity respectively after 2 h) are generated from the hydrogenolysis of the C-O bond in the THFA ring, while POH (11% of selectivity after 2 h) can either derive from the hydrodeoxygenation of 1,2-PDO and 1,5-PDO or from the hydrodeoxygenation of THFA and successive hydrogenolysis of the C-O bond. Only small amount of 2-methylfuran (MF) and 2-methyltetrahydroofuran (MTHF) were detected at any point of the reaction (less than 5% in total) along with other acetalization products (such as tetrahydrofurfural diethyl acetal and 5-hydroxpentanal diethyl acetal, hereafter identified as \"others\"). Figure 5: Fourier-transform infrared (FT-IR) spectra of pyridine recorded after evacuation at 150 \({}^{\circ}\)C (L = Lewis acid site band; B = Bronsted acid sites band) and normalised by the disk weight. (a) Pt/W-Nb\({}_{2}\)O\({}_{5}\), (b) Pt/Nb\({}_{2}\)O\({}_{5}\) and (c) Pt/Ti-Nb\({}_{2}\)O\({}_{5}\). \begin{table}
\begin{tabular}{c c} \hline \hline
**Catalyst** & **mmol\({}_{\text{P}}\)/g\({}_{\text{CAT}}\)** \\ \hline Pt/Nb\({}_{2}\)O\({}_{5}\) & 0.078 \\ Pt/W-Nb\({}_{2}\)O\({}_{5}\) & 0.191 \\ Pt/Ti-Nb\({}_{2}\)O\({}_{5}\) & 0.014 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Amount of adsorbed pyridine on Lewis site. The influence of the insertion of a second metal into the Nb\({}_{2}\)O\({}_{5}\) structure on the catalytic performance was then investigated. Pt/W-Nb\({}_{2}\)O\({}_{5}\) and Pt/Ti-Nb\({}_{2}\)O\({}_{5}\) were tested in the same reaction conditions as Pt/Nb\({}_{2}\)O\({}_{5}\) (50 \({}^{\circ}\)C and 5 bar of H\({}_{2}\)) and the results are reported in Figure 7. Considering that Pt nanoparticles showed a similar average size (1.0-1.5 nm), any difference in catalytic activity and selectivity among the niobia-based materials can be attributed to chemical-physical properties of the various supports. The catalyst that showed the highest activity towards the hydrogenation of furfural was Pt/W-Nb\({}_{2}\)O\({}_{5}\), with 88% of substrate being converted after only 15 min.