# Metal Carbides for Biomass Valorization
## 3 Application in Biomass Transformation
### Second-Generation Biomass
#### 3.2.1 Cellulose  
Cellulose from plant biomass can serve as a sustainable feedstock for fuels, chemicals and polymers that are currently produced from petroleum. The efficient conversion of biomass to valuable and sustainable fuels and chemicals is still a challenge. One attractive approach lies in the transformation of cellulose into levulinic acid (LA) by acid-catalyzed hydrolysis. LA is a versatile building block containing a ketone carbonyl group and an acidic carboxyl group. When cellulose with a high O/C ratio is transformed into fuels, an excess of oxygen must be removed. Alternatively, when cellulose is  
Figure 5: Yield and selectivity obtained from different vegetal oil hydrodeoxygation. Reproduced with permission from [40]. Copyright The Royal Society of Chemistry, 2011.  
transformed into oxygenates, most of the oxygen-functional groups in the cellulose are preserved in the target molecule, polyols for example. Sustainable production of fuels. LA has been accepted as a promising and sustainable platform molecule for further application in biorefineries [47]. Ideally, LA can be hydrogenated to \(\gamma\)-valerolactone (GVL), another platform molecule that finds application as a precursor for chemicals, solvent, fuel additives and fuel [48] (Figure 6). Hydrogenation of levulinic acid to \(\gamma\)-valerolactone over supported molybdenum carbide was reported by [PERSON] et al. [30]. For comparison, molybdenum carbide was supported on both active carbon and carbon nanotubes. The choice of alternative, cheap, non-noble catalysts was directed by the availability and price limitations of noble metal-based catalysts, which are the catalytic systems most often used for GVL production. Molybdenum carbide was chosen not only for its comparable catalytic behavior to precious metals [23; 49], but also for its mechanical strength, as well as its electrical and thermal conductivity. To highlight the influence of the support during the reaction, the reaction was carried out at different temperatures (100, 150 and 200 \({}^{\circ}\)C). The higher the temperature, the better the LA conversion with both catalysts (approximately 95% and over 99% for 20% Mo\({}_{2}\)C/CNT and 20% Mo\({}_{2}\)C/AC, respectively). With Mo\({}_{2}\)C/CNT, better conversion was obtained (at 200 \({}^{\circ}\)C, over 99% LA conversion against 15% at 100 \({}^{\circ}\)C) and the LA conversion was stable over 6 h in the three cases (Figure 7). Figure 6: Overall reaction pathway to produce \(\gamma\)-valerolactone (GVL). Figure 7: Levulinic acid conversion versus time over Mo\({}_{2}\)C/AC (**a**) and Mo\({}_{2}\)C/CNT (**b**) at 30 bar of H\({}_{2}\) and LSHV = 3 h\({}^{-1}\). Tests performed at 100 \({}^{\circ}\)C (**\(\blacksquare\)**), 150 \({}^{\circ}\)C (**\(\bullet\)**) and 200 \({}^{\circ}\)C (**\(\blacktriangle\)**). Reproduced with permission from [30]. Copyright The Royal Society of Chemistry, 2014. To better highlight the potential of Mo\({}_{2}\)C as an alternative to the noble metal-based catalysts, the authors performed the same reaction on a prepared 5 wt % Ru catalyst supported on AC (figure not shown). At 150 \({}^{\circ}\)C, 83% LA conversion was obtained versus a full conversion at 200 \({}^{\circ}\)C. The Ru/AC catalyst is therefore more active than Mo\({}_{2}\)C/CNT at 150 \({}^{\circ}\)C (83% versus 42% respectively) and similar results were obtained at 200 \({}^{\circ}\)C. CO chemisorption studies at 100 \({}^{\circ}\)C and 150 \({}^{\circ}\)C were carried out in order to better compare both catalysts. The number of metal active sites deriving from the CO chemisorption allows the calculation of the turnover frequency (TOF). At 150 \({}^{\circ}\)C, the TOF obtained for the LA hydrogenation to GVL were 10.3 h\({}^{-1}\), 4.5 h\({}^{-1}\) and 2.3 h\({}^{-1}\) for 20% Mo\({}_{2}\)C/CNT, 20% Mo\({}_{2}\)C/AC and 5% Ru/AC, respectively. 20% Mo\({}_{2}\)C/CNT exhibits a higher TOF than 5% Ru/AC.