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

Abstract

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 CoO x nanoislands on Pt(111) with different well-defined hydroxide structures are constructed that are more reactive than pristine CoO x nanoislands for CO oxidation, as confirmed by high-pressure scanning tunneling microscopy and X-ray photoelectron spectroscopy measurements. For hydrogenated CoO x / Pt(111) containing a Co−OH bilayer, hydroxyl O (O H ) and lattice O (O L ) modified by hydroxyl have a similar reactivity with CO. O H in hydroxylated CoO x /Pt(111) containing HO−Co−OH trilayer has a higher reactivity than O L . 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 CoO x /Pt catalysts in CO oxidation via the introduction of H 2 and H 2 O. 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.