Catalytic oxidations of volatile organic compounds (VOCs) (benzene, toluene and o-xylene) over 1 wt% Pd/gamma-Al2O3 catalyst were carried out to assess the properties and performance of the I'd based catalyst. The properties of the prepared catalysts were characterized by the Brunauer Emmett Teller(BET) surface area, H-2 chemisorption, X-ray photoelectron spectroscopy (XPS), X-ray diffraction (XRD), and transmission electron microscopy (TEM) analyses. The experimental results revealed a significant increase in VOCs conversion with the lapse of the reaction time at certain reaction temperatures. On the other hand, the hydrogen pretreated 1 wt% Pd/gamma-Al2O3 catalyst, whose shape of conversion curve is similar to the non pretreated catalyst, led the conversion curves for the total oxidation of VOCs to be shifted to lower temperature. It was also found that such increases in VOCs conversion were highly dependent on the oxidation state of Pd and the growth of Pd particles in the catalyst. In addition, in the case of the catalyst consisting of the same oxidation state (PdO/Pd2+ or Pd-0), the particle sizes possibly play a more important role in the catalytic activity. The activity order of 1 wt% Pd/gamma-Al2O3 catalyst with respect to the VOC molecule was o-xylene > toluene > benzene. (C) 2009 Elsevier B.V. All rights reserved.