Low-Temperature Oxidation of Methane on Rutile TiO₂(110): Identifying the Role of Surface Oxygen Species

Understanding the microkinetic mechanism underlying photocatalytic oxidative methane (CH₄) conversion is of significant importance for the successful design of efficient catalysts. Herein, CH₄ photooxidation has been systematically investigated on oxidized rutile(R)-TiO₂(110) at 60 K. Under 355 nm irradiation, the C-H bond activation of CH₄ is accomplished by the hole-trapped dangling O_Ti^- center rather than the hole-trapped O_b^- center via the Eley-Rideal reaction pathway, producing movable CH₃^• radicals. Subsequently, movable CH₃^• radicals encounter an O/OH species to form CH₃O/CH₃OH species, which could further dissociate into CH₂O under irradiation. However, the majority of the CH₃^• radical intermediate is ejected into a vacuum, which may induce radical-mediated reactions under ambient conditions. The result not only advances our knowledge about inert C-H bond activation but also provides a deep insight into the mechanism of photocatalytic CH₄ conversion, which will be helpful for the successful design of efficient catalysts.