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 O-2 with reduced TiO2(110)-(1 x 1) crystals. STM is the technique of choice to unravel the relation between vacancy and non-vacancy assisted O-2 dissociation channels as a function of temperature. It is revealed that the vacancy-assisted, first O-2 dissociation channel is preferred at low temperature (similar to 120 K), whereas the non-vacancy assisted, second O-2 dissociation channel operates at temperatures higher than 150 K-180 K. Based on the STM results on the two dissociative O-2 interaction channels and the TPD data, a new comprehensive model of the O-2 chemisorption on reduced TiO2(110) is proposed. The model explains the relations between the two dissociative and the molecular O-2 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 O-2 dissociation channels as well as the kinetics of the diffusion and reaction of Ti interstitials. (C) 2010 Elsevier B.V. All rights reserved.