Modulating catalytic oxygen activation over Pt–TiO2/SiO2 catalysts by defect engineering of a TiO2/SiO2 support

Abstract

Binary TiO₂/SiO₂ oxides were synthesized via flame spray pyrolysis as supports for a Pt catalyst. The effect of the mole ratio of the silica on the catalyst characteristics and catalytic performance for formic acid oxidation under dark (non-illuminated) conditions and following UV light pre-treatment was examined. As the TiO₂ : SiO₂ ratio increased, the following was observed: (i) the specific surface area gradually decreased from ∼325 m² g⁻¹ to ∼50 m² g⁻¹; (ii) the crystal structure was transformed from amorphous titania to crystalline anatase phase; (iii) the defect sites comprising Ti³⁺, E′ centres, and non-bridging oxygen hole centers (NBOHCs) were maximum at a TiO₂ : SiO₂ ratio of 1 : 2 (Pt/1TiO₂–2SiO₂); and (iv) oxygen adsorbed on the Pt deposit surface (PtO_ads) was a maximum for Pt/1TiO₂–2SiO₂. The catalytic activity of Pt–TiO₂/SiO₂ was strongly dependent on the TiO₂/SiO₂ ratio and was further enhanced by hydrogenation and UV light pre-treatment. In line with the greatest presence of support-based defects and PtO_ads species, the Pt/1TiO₂–2SiO₂ catalyst exhibited the highest catalytic rate following UV light pre-treatment. The simultaneously boosted presence of PtO_ads and defect sites (comprising Ti³⁺, E′ centers, and NBOHC) on the Pt–TiO₂/SiO₂ catalysts following UV-light pre-treatment is proposed as the origin of the enhanced formic acid oxidation reaction.