Adsorption and desorption kinetics of oxygen on tin–antimony oxide catalyst by quasi-constant coverage methods

Abstract

The determination of the parameters (activation energies and pre-exponential factors) characterizing the kinetics of adsorption or desorption of a gas on a surface by means of classical isothermal or temperature-programmed desorption methods is generally difficult in the case of heterogeneous adsorption states. It is shown that experimental techniques at quasi-constant surface coverages allow us to overcome the problem and to determine the dependence of the kinetic parameters on coverage. Application to the tin–antimony oxide catalyst (Sb/Sn = 4) showed that adsorbed oxygen occupies a continuous distribution of states. The amount of oxygen adsorbed represents 23% of an O^2– compact monolayer. Mean adsorption and desorption energies of activation are ca. 40 and 330 kJ mol^–1, respectively. A desorption frequency factor of the order of 10¹³–10¹⁴s^–1 and adsorption condensation coefficients of the order of 10^–7 have been found.