Study of oxygen desorption from SnO2: New possibilities through fast intermittent temperature-programmed desorption

Abstract

A differential desorption technique called intermittent temperature-programmed desorption (ITPD) was used to gain new information on the superficial oxygen species of SnO2 a solid used extensively for the preparation of sensors and redox catalysts. The use of an original device involving an induction heating system enabled the time necessary for ITPD determination to be decreased by a factor of 20 or so, compared to that with a classical apparatus. TPD and ITPD studies carried out in vacuum showed the existence of at least two distinct states desorbing at temperatures hiigher than 700 K. The corresponding amount of adsorbed oxygen was less than 10% of that necessary for the formation of a compact monolayer of oxide ions. These two states exhibited apparent activation energies of desorption, Eapp, equal to 285 ± 10 kJ/mol and 334 ± 8 kJ/ mol, respectively. The corresponding frequency factors, v, were far higher than 1013 s-1, indicating that re-adsorption was unlikely and that Eapp was equal to the activation energy for desorption, Ed. Calculations using a classical desorption rate expression showed that the ITPD profiles could be simulated and compared to the experimental data successfully.