Catalytic upgrading of pyroligneous acid, by-product from slow pyrolysis of woody biomass for char production, was carried out using zirconia-supported iron-oxide catalysts under a steam atmosphere at temperatures ranging from 623 to 723 K, and the effect of ZrO2 content in the ZrO2-FeOX catalysts on catalytic activity and ketone yields was investigated. It was demonstrated that hydroxyacetone and carboxylic acids (acetic and propionic acids) in the pyroligneous acid were converted into aliphatic ketones (acetone and 2-butanone) via a ketonization reaction over the ZrO2-FeOX catalyst. However, reaction inhibition by metal impurities in the pyroligneous acid such as potassium (K) and magnesium (Mg) was also observed. These metal impurities could be removed from the pyroligneous acid without changing the organic composition by using an ion-exchange resin. The removal of the metal impurities was effective in increasing the ketone yields. Moreover, as the W/F value (W: Amount of catalyst, and F: Flow rate of the pyroligneous acid in the feed) increased, the ketone yield increased up to approximately 30 C mol%, and the ketone fraction in the liquid product reached 55 C mol%. (C) 2011 Elsevier Ltd. All rights reserved.