Dissociative and molecular oxygen chemisorption channels on reduced rutile TiO2(110): An STM and TPD study

High-resolution scanning tunneling microscopy (STM) and temperature-programmed desorption (TPD) were used to study the interaction of O2 with reduced TiO2(110)–(1 × 1) crystals. STM is the technique of choice to unravel the relation between vacancy and non-vacancy assisted O2 dissociation channels as a function of temperature. It is revealed that the vacancy-assisted, first O2 dissociation channel is preferred at low temperature (~ 120 K), whereas the non-vacancy assisted, second O2 dissociation channel operates at temperatures higher than 150 K–180 K. Based on the STM results on the two dissociative O2 interaction channels and the TPD data, a new comprehensive model of the O2 chemisorption on reduced TiO2(110) is proposed. The model explains the relations between the two dissociative and the molecular O2 interaction channels. The experimental data are interpreted by considering the available charge in the near-surface region of reduced TiO2(110) crystals, the kinetics of the two O2 dissociation channels as well as the kinetics of the diffusion and reaction of Ti interstitials.