This study investigated the effect of relative humidity on HCHO oxidation at room temperature over Pt/TiO2 catalysts prepared by wet impregnation. Atmospheric moisture acts as a promoter that increases the catalytic activity of the formaldehyde oxidation reaction. From DRIFTs, it was confirmed that the excellent performance was caused by the hydroxyl group resulting from the presence of moisture. The hydroxyl group on the catalyst surface could be recovered by atmospheric oxygen. Surface OH or lattice oxygen could be used for adsorption and conversion of HCHO into formate even if atmospheric oxygen was not present. Adsorbed formate could be oxidized into CO2 and H2O using the surface OH or OH from H2O. The Pt/TiO2 catalyst prepared in this study showed excellent activity and could completely remove HCHO at room temperature. It was also confirmed that HCHO could be oxidized by our catalyst even when using a small quantity of Pt (0.1 wt%). (C) 2014 Elsevier B.V. All rights reserved.