CO Oxidation at Low Temperatures over the Au Cluster Supported on Crystalline Silicotitanate

Crystalline silicotitanate (CST) with a sitinakite structure has attracted considerable attention as an ion exchanger because of its anionic surface owing to SiO₄ tetrahedral and TiO₆ octahedral linked structures. In particular, the anionic surface of CST is advantageous in immobilizing single Au atoms derived from a cationic precursor such as Au(en)₂Cl₃ (en = ethylenediamine). In this study, a Au/CST catalyst was prepared and evaluated for CO oxidation. The transmission electron microscopy and X-ray photoelectron spectroscopy results suggest that Au single atoms and clusters (Au^δ+, 0 < δ < 1) were supported on Na⁺-CST particles. The 1.0 wt % Au/CST catalyst yielded high catalytic activity for CO oxidation, where 50% CO oxidation was achieved at a low temperature of -13 °C. In the low-temperature region (from -84 to 20 °C), CO oxidation over Au/CST may progress through the well-known Langmuir-Hinshelwood mechanism. Conversely, the experimental results of CO oxidation without O₂ confirmed that the reaction proceeded according to the Au-assisted Mars-van Krevelen mechanism using the lattice oxygens of the CST particles at temperatures above 20 °C. Therefore, this work contributes to the design of highly dispersed single-atom or cluster catalysts using the anionic surface of the microporous CST.