# Metal Carbides for Biomass Valorization
## 3 Application in Biomass Transformation
### Second-Generation Biomass
#### 3.2.1 Cellulose
Unsupported Mo\({}_{2}\)C was either prepared by the physical mixture of molybdenum oxide, MoO\({}_{3}\), and CNTs or by using nanostructured \(\alpha\)-MoO\({}_{3}\) as a precursor. The catalysts obtained after carburization were labeled Mo\({}_{2}\)C\(\_\)PM and Mo\({}_{2}\)C\(\_\)N, respectively. They were further tested, together with commercial MoO\({}_{3}\), during aqueous phase LA hydrogenation. All catalysts were active. After 6 h reaction, 20%, 45% and 60% LA conversion was obtained for Mo\({}_{2}\)C\(\_\)PM, Mo\({}_{2}\)C\(\_\)C and Mo\({}_{2}\)C\(\_\)N, respectively [35]. For a better understanding of the catalytic performance, CO chemisorption was carried out. The nature of the active sites is similar in both synthesized catalysts, but the preparation method influenced the total number of sites. Despite a higher surface area, Mo\({}_{2}\)C\(\_\)PM presented a lower CO uptake and catalytic activity compared to the nanostructured Mo\({}_{2}\)C\(\_\)N. On Mo\({}_{2}\)C\(\_\)PM, agglomeration of well-orientated \(\beta\)-Mo\({}_{2}\)C nanoparticles implies a higher surface area, as well as a coating of particles by a thin layer of carbon [50; 51]. The results of this research underlined the importance of the control over the particle morphology and size, compared to the surface area in unsupported molybdenum carbide for LA hydrogenation. From both examples, molybdenum carbide, unsupported or supported, can be a valid candidate for replacing noble metal-based catalysts in the hydrogenation of LA. _Sustainable production of chemicals._ Ethylene glycol (EG), is the monomer for the large-scale manufacture of poly(ethylene terapitalate) (PET) fibers and bottles [52]. [PERSON] et al. reported on the catalytic conversion of cellulose to EG over supported carbide catalysts [53]. The reaction was carried out over 2.5% Pt/AC, W\({}_{2}\)C/AC-800 (30 wt % tungsten nominal value) and Mo\({}_{2}\)C/AC-700 (30 wt % molybdenum nominal value). W\({}_{2}\)C/AC-800 and Mo\({}_{2}\)C/AC-700 are active carbon tungsten carbide catalyst carburized at 800 \({}^{\circ}\)C and molybdenum carbide supported on active carbon carburized at 700 \({}^{\circ}\)C, respectively. The difference in the carburization temperature depends upon the temperature at which the corresponding pure phase is reached. The catalytic transformation of cellulose was performed at 245 \({}^{\circ}\)C, at an initial H\({}_{2}\) pressure of 6 MPa for 0.5 h. The catalysts were active, 98% and 85% cellulose conversion was obtained for W\({}_{2}\)C/AC-800 and Mo\({}_{2}\)C/AC-700, respectively. The cellulose conversion was calculated via the cellulose weight difference before and after reaction. Pt/AC was less active (66%) than the carbide catalysts. 27.4%, 8.2% and 5.3% EG yield was obtained for W\({}_{2}\)C/AC-800, Pt/AC and Mo\({}_{2}\)C/AC-700, respectively. A low EG yield was obtained over Mo\({}_{2}\)C/AC-700, which formed more unsaturated acids, due to an incomplete hydrolysis of cellulose. The high selectivity to EG, instead of sorbitol, demonstrates that the reaction involves not only the hydrolysis of cellulose to glucose and the hydrogenation of glucose to sorbose, but also the cleavage of the C-C bonds. To highlight the effect of the metal active phase and the support itself, the authors moved to alumina as the support. Tungsten carbide or molybdenum carbide supported catalysts were poorly selective to polyols. Mesoporous carbon (MC) was also used as a support to disperse tungsten carbide (WC\({}_{\rm x}\)) by [PERSON] et al. and 73% EG yield was reached [54]. MC might facilitate the hydrogenation activity of the unsaturated intermediates formed during the conversion of cellulose to EG. Dispersion and accessibility of active components of WC\({}_{\rm x}\) could be favored by the 3D interconnected mesoporous structure. Hot water and the tungsten oxide surface might provide the acid sites necessary for cellulose hydrolysis [55], while the platinum-like electronic properties of tungsten carbide deliver the hydrogenation sites [18].