A method is disclosed for converting biomass into a fuel additive, the method comprising: liquefying the biomass to form a liquor; neutralizing the liquor; precipitating lignin out of the liquor; extracting furfural (FF) and 5-hydroxymethylfurfural (HMF) from the liquor; and hydrodeoxygenating (HDO) the extracted furfurals over a Cu—Ni/TiO2 catalyst. The catalyst for hydrodeoxygenating (HDO) furfural (FF) and 5-hydroxymethylfurfural (HMF) to methylated furans comprises copper-nickel (Cu—Ni) particles supported on titanium dioxide (TiO2), and wherein the copper-nickel particles form core-shell structures in which copper (Cu) is enriched at a surface of the catalyst.