Ag Clusters on Titanium Oxides under Metal–Support Interactions for the Catalytic Oxidation of CO at Room Temperature

Silver-loaded titanium oxide catalysts were synthesized via flame spray pyrolysis (FSP) and evaluated for their CO oxidation activity. X-ray diffraction and X-ray photoelectron spectroscopy revealed that the FSP-prepared catalysts contained substoichiometric TiO x ( x < 2), which was formed through interactions between titanium oxides and Ag during FSP synthesis. These interactions led to the formation of cationic Ag, as confirmed by X-ray photoelectron and Auger electron spectroscopies. Furthermore, these interactions suppressed the sintering of small Ag clusters (<3 nm). The small Ag size and cationic oxidation state induced by these interactions enhanced catalytic activity. The FSP-prepared catalysts exhibited a higher CO oxidation activity than a wet-prepared catalyst. In particular, the FSP-prepared catalyst containing 20 wt % Ag demonstrated 18% CO conversion at room temperature under a flow rate of 6 × 10 4 mL STP h –1 g cat –1 and maintained its catalytic activity over multiple cycles of use. The amount of reactive oxygen species (ROS), which are involved in oxidation reactions, was evaluated by using H 2 pulse titration. Notably, FSP-prepared catalysts generated more ROS than the wet-made catalyst. Furthermore, while ROS in the FSP-prepared catalysts can be regenerated upon exposure to oxygen, the wet-made catalyst is not endowed with this regenerative ability. These findings demonstrate that unique flame-induced interactions are crucial for achieving high catalytic activity and durability. Therefore, FSP is a promising and scalable method for the fabrication of efficient Ag catalysts.