CO Oxidation at\nLow Temperatures over the Au Cluster\nSupported on Crystalline Silicotitanate

Crystalline silicotitanate (CST) with a sitinakite structure\nhas\nattracted considerable attention as an ion exchanger because of its\nanionic surface owing to SiO<sub>4</sub> tetrahedral and TiO<sub>6</sub> octahedral linked structures. In particular, the anionic surface\nof CST is advantageous in immobilizing single Au atoms derived from\na cationic precursor such as Au(en)<sub>2</sub>Cl<sub>3</sub> (en\n= ethylenediamine). In this study, a Au/CST catalyst was prepared\nand evaluated for CO oxidation. The transmission electron microscopy\nand X-ray photoelectron spectroscopy results suggest that Au single\natoms and clusters (Au<sup>δ+</sup>, 0 < δ < 1)\nwere supported on Na<sup>+</sup>–CST particles. The 1.0 wt\n% Au/CST catalyst yielded high catalytic activity for CO oxidation,\nwhere 50% CO oxidation was achieved at a low temperature of −13\n°C. In the low-temperature region (from −84 to 20 °C),\nCO oxidation over Au/CST may progress through the well-known Langmuir–Hinshelwood\nmechanism. Conversely, the experimental results of CO oxidation without\nO<sub>2</sub> confirmed that the reaction proceeded according to the\nAu-assisted Mars–van Krevelen mechanism using the lattice oxygens\nof the CST particles at temperatures above 20 °C. Therefore,\nthis work contributes to the design of highly dispersed single-atom\nor cluster catalysts using the anionic surface of the microporous\nCST.