Mechanistic study on formaldehyde removal over Pd/TiO2 catalysts: Oxygen transfer and role of water vapor

• Highly efficient Pd nanoparticles were facilely synthesized by precipitation followed by NaBH4 reduction.
• Complete oxidation of HCHO was achieved at room temperature on the 0.1 wt% Pd–TiO2.
• The precipitated Pd shows strong capacity for generation and transfer of active oxygen.
• Water vapor is essential to HCHO oxidation since it favors the transfer of oxygen.

It has become a hot topic to destroy air pollutants such as formaldehyde (HCHO) using noble metal nanoparticles at ambient temperature. To reduce noble metal loading for saving cost and investigate the reaction mechanism presents two challenges for this reaction. In this study, highly efficient Pd/TiO2 catalysts were facilely synthesized with deposition–precipitation method followed by sodium borohydride (NaBH4) reduction at room temperature. XPS, H2-TPR and O2-TPD experiments were used to identify the oxygen species on the catalysts. Complete oxidation of HCHO can be achieved at ambient temperature over them even with 0.1 wt% Pd loading. The Pd/TiO2 catalysts prepared by deposition–precipitation method is much more active than those prepared by impregnation method mainly due to the stronger capacity for the generation and transfer of chemisorbed oxygen. Water vapor is essential to HCHO oxidation. Hydroxyl radical (OH) from water vapor dissociation favors the adsorption and transfer of oxygen on the Pd/TiO2 catalysts, which is very important during HCHO oxidation.