Spectroscopic Studies of How Moisture Enhances CO Oxidation over Au/BN at Ambient Temperature

Gold catalysts readily catalyze CO oxidation at subambient temperature, wherein moisture can influence the activity, typically with a volcano-shaped dependence. In this study, we examine moisture-enhanced CO oxidation over Au/BN. The room-temperature CO oxidation activity of Au/BN increases quickly with increasing moisture content up to 100% relative humidity (RH). In situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) and in situ UV–vis diffuse reflectance spectroscopy (UV-vis-DRS) demonstrate that mainly metallic gold is present on the h-BN support. Surface intermediates are found when moisture is fed together with CO and O2, attributable to *CO­(H2O) n and *OOH, respectively. These surface intermediates are reactive when counter-reactant is purged. Injection of isotope-labeled H2 18O demonstrates that OH from H2O takes part in the process of CO2 formation. The results of this study provide direct evidence showing moisture-enhanced CO adsorption, moisture-enhanced O2 adsorption, and their activation that can possibly lead to promotion of CO oxidation over the Au/BN catalyst.