Dissociative and molecular oxygen chemisorption channels on reduced rutile TiO 2(110): An STM and TPD study

Abstract

High-resolution scanning tunneling microscopy (STM) and temperature-programmed desorption (TPD) were used to study the interaction of O 2 with reduced TiO 2(110)–(1 × 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 (~ 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 TiO 2(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 TiO 2(110) crystals, the kinetics of the two O 2 dissociation channels as well as the kinetics of the diffusion and reaction of Ti interstitials.