Molybdenum carbide catalysts supported on carbon nanofibers (β-Mo 2 C/CNF) were synthetized employing different carburization parameters: five temperatures (550-750 ºC) and four heating rates (1-10 ºC/min) were tested. The carburization process of the Mo precursor in the catalysts was studied by thermogravimetric analysis, X-ray diffraction, X-ray photoelectron spectroscopy, N 2 physisorption, inductively coupled plasma optical emission spectrometry and transmission electron microscopy. The formation of the carbide phase was confirmed by the presence of the oxycarbide and carbide phases which were observed on the surface of all catalysts. Higher carburization temperatures resulted in an increase of the carbide phase content and crystal size at the expenses of the oxycarbide phase disappearance. High carburization temperatures and low heating rates were needed in order to obtain well-defined β-Mo 2 C crystals over the

In this work, a Mo 2 C catalyst that was supported on commercial carbon nanofibers (CNF) was synthetized and tested in the hydrodeoxygenation (HDO) of guaiacol. The effects of operating conditions (temperature and pressure) and reaction time (2 and 4 h) on the conversion of guaiacol and products selectivity were studied. The major reaction products were cresol and phenol, followed by xylenols and toluene. The use of more severe operating conditions during the HDO of guaiacol caused a diversification in the reaction pathways, and consequently in the selectivity to products. The formation of phenol may have occurred by demethylation of guaiacol, followed by dehydroxylation of catechol, together with other reaction pathways, including direct guaiacol demethoxylation, and demethylation of cresols. X-ray diffraction (XRD) analysis of spent catalysts did not reveal any significant changes as compared to the fresh catalyst.

This work firstly provides a thorough insight into the effects of the operating conditions (catalyst loading, initial H 2 pressure temperature, reaction time, H 2 /guaiacol ratio and liquid reaction volume) on the hydrodeoxygenation (HDO) of guaiacol over a Mo 2 C/CNF catalyst. Under the operating condition tested, gas and solid formation was negligible and guaiacol was primary converted to different liquid products, including non-deoxygenated (0-oxy), mono-deoxygenated (1-oxy) and fully deoxygenated (2oxy) compounds, together with high molecular weight soluble oligomers. An increase in the catalyst loading increased the guaiacol conversion and HDO efficiency, augmenting the proportions of HDO products. Among these species, the progressive transformation of 1-oxy compounds into 2-oxy species was kinetically and thermodynamically controlled by the catalyst loading and the amount of H 2 dissolved in the liquid medium, respectively. Augmenting the H 2 pressure increased the H 2 availability in the liquid, which led to increases over time in the guaiacol conversion and HDO efficiency, thus promoting the production of HDO products and facilitating the transformation of guaiacol into fully de-oxygenated products. This increase depended on the reaction volume, with more pronounced variations occurring for a small than for a large volume due to the greater variations occurring in the H 2 /guaiacol ratio for the former than the latter. The temperature exerted a kinetic promoting effect together with a thermodynamic inhibitory influence, as some of the reactions involved were not thermodynamically favoured at high temperature. Therefore, the detailed analysis included in this work brings novel information on guaiacol HDO, which can help to establish the basis for catalysts development and reactors design to achieve a sustainable bio-fuels production from lignocellulosic bio-oils.

Carbon nanofiber (CNF) supported β-Mo 2 C-based catalysts were synthetized by carbothermal hydrogen reduction at 750 ºC for different times (1, 2, 4, 6 and 18 h) in order to study both the carbide phase formation and the CNF stability during this key stage. Catalysts were characterized by N 2 physisorption, X-ray diffraction (XRD), X-ray specific surface area. In the guaiacol HDO reaction, higher conversions (72-80 %) and HDO ratios (53-63 %) were obtained using catalysts carburized for 2 h and onwards.Considering the carbide content in the catalyst, 1 and 2 h carburized catalysts exhibited the highest values of formation of HDO products: phenol, cyclohexane + benzene and anisole. Besides this, a clear relationship between the Mo 2 C surface area () and the product formation rate could be inferred for the catalysts carburized at 1, 2 and 4 h, in which the textural properties were not affected by the carburization time. On the other hand, longer carburization times had a worse performance despite the largest values of , being this fact related to the dramatic loss of the catalyst textural properties.

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