Pd-supported tungsten oxide ( Pd/WO3) was prepared by photodeposition by using black light. X-ray diffraction and X-ray photoelectron spectroscopy analyses of Pd/WO3 confirmed the presence of Pd(0). Pd(0) was uniformly dispersed on the surface of WO3. The optimum Pd amount for the degradation of aqueous methylene blue (MB) was 0.5 wt%, and the photocatalytic activity in this case was 27 times higher than that of pure WO3. The optimum Pd amount for the decomposition of gaseous acetaldehyde was 0.1 wt%, and the photocatalytic activity using this amount of Pd was 5.9 times greater than that for pure WO3. Pd as a support improved the charge separation efficiency. Further, hydrogen peroxide was produced on the Pd(0) side of the photocatalyst because of the movement of photoexcited electrons, and it contributed significantly to MB degradation. Moreover, electrons produced with MB moved to the Pd side, and contributed to hydrogen peroxide production. Only photocatalytic degradation contributed to acetaldehyde decomposition, while both photocatalytic and self-sensitized degradation contributed to MB degradation. The Pd/WO3 sample containing the optimal amount of Pd acted as an effective photocatalyst, despite the difference between the optimal Pd amount required for acetaldehyde decomposition and that for MB degradation. (C) 2014 Elsevier B.V. All rights reserved.