Upgrading of high-boiling fraction of bio-oil in supercritical methanol

► Supercritical methanol condition could greatly facilitate the esterification process. ► Esterification and cracking (hydrocracking and alcoholysis) were the two dominant processes during the upgrading reactions. ► PtNi/MgO gave a high yield (72.4 wt.%) of desired product, but led to coke formation. ► Al2(SiO3)3 supported catalysts tended not to form coke, which would improve the catalyst life. ► The refined oil is believed to be a potential fossil transportation fuel additive.