Uncovering Molecular and Kinetic Insights into the Art of Catalyst Synthesis by Strong Electrostatic Adsorption Using <i>In Situ</i> ATR-IR Spectroscopy

Single-atom catalysts, which consist of isolated metal sites immobilized on the support, have attracted significant attention in heterogeneous catalysis due to their high catalytic performance. The so-called strong electrostatic adsorption (SEA), in which a metal precursor is deposited onto an oxide support by electrostatic attraction, is widely employed to obtain single-atom catalysts in wet synthesis. In this work, we investigated the adsorption behavior of Re precursor, perrhenate, on anatase titania as an example of SEA studied by <i>in situ</i> attenuated total reflection infrared (ATR-IR) spectroscopy. The study confirms that the adsorption of perrhenate on titania is enhanced at a lower pH, which is consistent with a SEA model, and that the adsorption and desorption processes are reversible at pH 3.0. The ATR-IR spectroscopic kinetic analysis of the adsorption processes of perrhenate in nitric acid, assuming the Langmuir adsorption model, reveals that the kinetics of the perrhenate adsorption onto titania is influenced by the ionic strength. Furthermore, the adsorption mechanism of perrhenate changes depending on pH between 3.0 and 5.0. This study demonstrates that <i>in situ</i> ATR-IR spectroscopy is a powerful tool for the real-time monitoring and the kinetic study of SEA processes to design atomically engineered catalytic active sites.