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

Abstract

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 (OTi) to adjacent Pt single atoms. This leads to the formation of low-valence Pt and unsaturated-charge OTi 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 OTi sites and NO, thereby facilitating NO activation. The designed single-atom catalysts with synergistic sites exhibit unmatched activity at low temperatures (above 90% NOx conversion at 100 °C), along with higher turnover frequency value (0.74 s-1) and superior stability, making them potentially suitable for industrial applications.