Bio-oil upgrading in supercritical water using Ni-Co catalysts supported on carbon nanofibres

6 Figures, 9 Tables.-- © 2016. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/This work addresses the preparation, characterisation and screening of different Ni-Co catalysts supported on carbon nanofibres (CNFs) for use in the upgrading of bio-oil in supercritical water. The aim is to improve the physicochemical properties of bio-oil so that it can be used as a fuel. The CNFs were firstly oxidised in HNO3 and afterwards subjected to a thermal treatment to selectively modify their surface chemistry prior to the incorporation of the metal active phase (Ni-Co). The CNFs and the supported catalysts were thoroughly characterised by several techniques, which allowed a relationship to be established between the catalyst properties and the upgrading results. The use of Ni-Co/CNFs for bio-oil upgrading in supercritical water (SCW) significantly improved the properties of the original feedstock. In addition, the thermal treatment to which the fibres were subjected exerted a significant influence on their catalytic properties. An increase in the severity of the thermal treatment led to a substantial reduction in the oxygen content of the CNFs, mainly due to the removal of the less stable oxygen surface groups, which allowed their surface polarity to decrease. This decrease resulted in less formation of solid products. However, it also reduced the H/C and increased the O/C ratios of the upgraded liquid. Therefore, a compromise between the yield and the properties of the upgraded bio-oil was achieved with a Ni-Co supported on a CNF with a moderate amount of oxygen surface groups.The authors wish to express their gratitude to the Aragon Government (GPT group), the European Social Fund and the Spanish MINECO (projects ENE2010-18985, ENE 2011-28318, ENE2013-41523-R and ENE2014-52189-C2-1-R) for providing financial support. Javier Remón Núñez would like to express his gratitude to the Spanish MINECO for the FPI (BES-2011-044856) and mobility (EEBB-I-14-08688) grants awarded. Jose Luis Pinilla thanks the Spanish MINECO for his Ramon y Cajal research contract.Peer reviewe