Design and synthesis of Pt/TiO₂ catalyst with abundant surface hydroxyl for formaldehyde oxidation

Catalytic oxidation of formaldehyde (HCHO) is a highly effective method for indoor HCHO removal. However, many aspects of the catalytic mechanism remain unclear, making the optimization of catalysts largely empirical. Herein, we report a coupled experimental and computational study of Pt/TiO₂ catalysts, with special focus on the functional roles of surface oxygen vacancies and hydroxyl groups in the catalytic oxidation of HCHO. DFT calculations combined with control experiments revealed that the formation of surface oxygen vacancies on TiO₂ and their capability in facilitating H₂O dissociation are strongly dependent on the exposed facets. Correlating these facet-dependent properties with the determined activity further indicated that the catalytic performance is directly related to the abundance of surface hydroxyl groups, rather than surface oxygen vacancies as commonly assumed. Guided by these insights, we employed a combination of facet-engineering and alkali metal modification strategies to design a potassium-modified Pt/TiO₂ catalyst with predominantly exposed {100} facets (denoted as Pt/TiO₂{100}-K). The Pt/TiO₂{100}-K catalyst showed an impressively high mass-specific reaction rate of 105.7 μmol g_Pt^-1 s^-1, along with fairly good stability and moisture tolerance. Further investigations using in situ DRIFTS coupled with on-line GC provided additional insight into the reaction mechanism of HCHO oxidation over the Pt/TiO₂{100}-K catalyst.