# Metal Carbides for Biomass Valorization
## 3 Application in Biomass Transformation
### First-Generation Biomass  
The pyrolysis of raw biomass results in the production of bio-oil. The hydrolysis reaction of fats and oils, also called triglycerides, results in the production of glycerol and fatty acids which are carboxylic acids characterized by a high O/C ratio. Once the excess oxygen atoms are removed, these hydrocarbon chains, in the diesel range, constitute possible renewable feedstocks for transportation fuels. HDO reaction has thus gained much attention in making suitable triglycerides as an alternative fuel precursor to replace diesel from fossil sources. Carbon nanotube-supported Mo\({}_{2}\)C (Mo\({}_{2}\)C/CNT) and active carbon-supported Mo\({}_{2}\)C (Mo\({}_{2}\)C/AC) catalysts were reported as active and selective in the one-step conversion of vegetable oils into branched diesel-like hydrocarbons [40; 44]. When supported on AC, Mo\({}_{2}\)C was found to be more active than the unsupported Mo\({}_{2}\)C for the HDO of methyl stearate, a model compound [44]. After only 1 h reaction, Mo\({}_{2}\)C/AC reaches 65% conversion. Similar conversion (67%) was reached with the unsupported Mo\({}_{2}\)C after 5 h. Both catalysts led to the formation of paraffins via HDO, 42% versus 69% selectivity with Mo\({}_{2}\)C and Mo\({}_{2}\)C/AC, respectively. Mo\({}_{2}\)C/AC was therefore utilized as catalyst for the conversion of diverse vegetable oils (such as, among others, soybean oil, rapeseed, olive oil and sunflower oil) into hydrocarbons. The highest yield of hydrocarbon was obtained with olive oil (88%), while sunflower oil as feedstock led to a lower yield, 76%. Mo\({}_{2}\)C/AC was found to be active and stable over sixteen runs with olive oil as feedstock. 20% Mo\({}_{2}\)C/CNT was tested and compared to 5% Pd/CNTs and 5% Pt/CNTs for the one-step hydrodeoxygenation and isomerization of vegetable oils (Scheme 2) [40]. 20% Mo\({}_{2}\)C/CNTs was more active than 5% Pd/CNTs and 5% Pt/CNTs (90%, 41% and 32%, respectively) in the transformation of methyl palmitate at 240 \({}^{\circ}\)C. The authors observed that the main reaction route of higher aliphatic esters on Mo\({}_{2}\)C is hydrodeoxygenation, compared to noble metals (Scheme 1). The authors further investigated the HDO of vegetable oils catalyzed with 20% Mo\({}_{2}\)C/CNTs. The highest paraffin yields were obtained (86%) when rapeseed oil was used as feedstock (Figure 5). Surprisingly, the catalyst was also selective to branched alkanes including 2-methylheptadecane, 3-methylheptadecane, 4-methylheptadecane, 8-methylheptadecane and 2,6,10-trimethylpentadecane. Branched alkanes are high-grade diesel fuels with a low freezing point. The authors postulated that the isomerization reaction of linear alkanes into branched alkanes on Mo\({}_{2}\)C/CNTs catalysts was possible thanks to the structure of esters, especially the length of the carbon chains. Compared to rapeseed oil, a similar hydrocarbon yield (87%) and higher branched alkane yield (55%) were obtained with sunflower oil by reducing the mass ratio of sunflower oil with Mo\({}_{2}\)C to 7.5:1. **Scheme 2. ** Hydrodeoxygenation of higher aliphatic esters on Mo\({}_{2}\)C/CNTs. Reproduced with permission from [40]. Copyright The Royal Society of Chemistry, 2011. Mo\({}_{2}\)C/CNT exhibited better catalytic performance compared to noble metal (5% Pd and 5% Pt) supported catalysts, the classical catalyst for the transformation of the model compound methyl palmit into hydrocarbons, (conversion of 90%, 41% and 32% for Mo\({}_{2}\)C/CNTs, Pd/CNTs and Pt/CNTs, respectively) as well as a higher resistance to deactivation. Carbon nanofibers were investigated as a support for Mo\({}_{2}\)C and W\({}_{2}\)C by [PERSON] et al. [45] for the hydrodeoxygation of oleic acid. Both catalysts showed a good activity, but a different selectivity. Mo\({}_{2}\)C/CNF was selective to paraffin (saturated carbon) whereas W\({}_{2}\)C/CNF was more selective to olefin. Moreover, Mo\({}_{2}\)C/CNF was reported more active and more stable than W\({}_{2}\)C/CNF.