Enhancement of Pt-O Synergistic Sites through Titanium Vacancies for Low-Temperature Nitrogen Oxide Reduction

Improving the reaction rate of each step is significant for accelerating the multistep reaction of NO reduction by H₂. However, simultaneously enhancing the activation of different gaseous reactants using single-atom catalysts remains a challenge to maximize the activity. Herein, we propose a strategy that utilizes titanium-vacancy-regulated electronic properties of single atoms and defective support (Pt₁/d-TiO₂) to facilitate electron transfer from edge-share O atoms (O_Ti) to adjacent Pt single atoms. This leads to the formation of low-valence Pt and unsaturated-charge O_Ti sites, which causes the catalytic reaction to follow a synergistic mechanism. Specifically, experimental and theoretical analyses demonstrate that low-valence Pt sites finely tune the adsorption of H₂ molecules, consequently lowering the dissociation energy from 0.15 to as low as 0.01 eV. Moreover, using quasi-in situ spectroscopy, we clearly observe NO molecules being adsorbed on interfacial oxygen sites of a defective support. Then, the bond energy of the N-O bond is weakened through an electron acceptance-donation mechanism between unsaturated-charge O_Ti sites and NO, thereby facilitating NO activation. The designed single-atom catalysts with synergistic sites exhibit unmatched activity at low temperatures (above 90% NO_x conversion at 100 °C), along with higher turnover frequency value (0.74 s^-1) and superior stability, making them potentially suitable for industrial applications.