Alkali metal compounds have also been widely employed as catalysts in direct liquefaction of agricultural/forest biomass to suppress the formation of char (residue) and to enhance the yield of liquid products [24]. As expected, the presence of NaOH and Na2CO3 in the liquefaction of rice husk both dramatically enhanced the organic conversion. At the same time, the bio-oil production was remarkably promoted. Furthermore, according to Fig. 5, the catalytic effect of NaOH was better than Na2CO3. The superior effect of NaOH for promoting bio-oil production and suppressing the formation of SR may suggest that NaOH can be a promising catalyst for catalytic liquefaction of rice husk using ethanol as solvent. The high
activity of NaOH might be related to its strong alkalinity, facilitating the hydrolysis of polymers through the rupture the glycosidic bonds in cellulose and hemicellulose and the ester bonds in lignin [28].