Hydroxide Structure-Dependent OH Promotion Mechanism over a Hydroxylated CoOx/Pt(111) Catalyst toward CO Oxidation

Hydroxyl is ubiquitous in heterogeneous catalysis and significantly affects the catalytic performance of many important reactions. However, the complexity of practical catalysts makes direct investigation of the role of hydroxyl very challenging. In this work, partially hydroxylated CoOx nanoislands on Pt(111) with different well-defined hydroxide structures are constructed that are more reactive than pristine CoOx nanoislands for CO oxidation, as confirmed by high-pressure scanning tunneling microscopy and X-ray photoelectron spectroscopy measurements. For hydrogenated CoOx/Pt(111) containing a Co–OH bilayer, hydroxyl O (OH) and lattice O (OL) modified by hydroxyl have a similar reactivity with CO. OH in hydroxylated CoOx/Pt(111) containing HO–Co–OH trilayer has a higher reactivity than OL. In addition, the oxygen species located at edges of the nanoislands are more active than those located in the interior. The distinct OH promotion mechanisms are accordingly proposed, which are exploited to dramatically enhance the performance of real CoOx/Pt catalysts in CO oxidation via the introduction of H2 and H2O. These results provide insights into the relationship between the hydroxide structure, OH promotion mechanism, and catalytic reactivity, which contribute to the rational design of highly efficient catalysts.