Production of renewable fuels and chemicals from lignocellulosic biomass has attracted increasing attention because of decreasing oil reserves, enhanced fuel demand worldwide, increased climate concerns, and the inherent conflict between food prices and converting edible carbohydrates to ethanol or plant oils to bio-diesel [1-4]. Bio-oils, the liquid products obtained from biomass fast pyrolysis or liquefaction, are regarded as promising renewable energy sources by the virtue of their environmentally friendly potential [5,6]. Nonetheless, several drawbacks of bio-oil severely limit its potential to replace or supplement high-grade transportation fuels. These include low heating values, high corrosiveness, high water

content, thermal instability and immiscibility with hydrocarbon fuels etc. [7]. Thus, bio-oil has to be upgraded before using it as a fuel.