A comparative study of TiO2 supported noble metal catalysts for the oxidation of formaldehyde at room temperature

The TiO2 supported noble metal (Au, Rh, Pd and Pt) catalysts were prepared by impregnation method and characterized by means of X-ray diffraction (XRD) and BET. These catalysts were tested for the catalytic oxidation of formaldehyde (HCHO). It was found that the order of activity was Pt/TiO2 ≫ Rh/TiO2 > Pd/TiO2 > Au/TiO2 ≫ TiO2. HCHO could be completely oxidized into CO2 and H2O over Pt/TiO2 in a gas hourly space velocity (GHSV) of 50,000 h−1 even at room temperature. In contrast, the other catalysts were much less effective for HCHO oxidation at the same reaction conditions. HCHO conversion to CO2 was only 20% over the Rh/TiO2 at 20 °C. The Pd/TiO2 and Au/TiO2 showed no activities for HCHO oxidation at 20 °C. The different activities of the noble metals for HCHO oxidation were studied with respect to the behavior of adsorbed species on the catalysts surface at room temperature using in situ DRIFTS. The results show that the activities of the TiO2 supported Pt, Rh, Pd and Au catalysts for HCHO oxidation are closely related to their capacities for the formation of formate species and the formate decomposition into CO species. Based on in situ DRIFTS studies, a simplified reaction scheme of HCHO oxidation was also proposed.