The Temperature-Programmed Desorption of Oxygen from an Alumina-Supported Silver Catalyst

Abstract

The associative desorption kinetics of O2 from a 15 wt% Ag/α-Al2O3 atalyst were studied under atmospheric pressure in a microreactor set-up by performing temperature-programmed desorption (TPD) experiments. Saturation with chemisorbed atomic oxygen (O*) was achieved by dosing O2 for 1 h at 523 K and at atmospheric pressure followed by cooling in O2 to room temperature. The TPD spectra showed almost symmetric O2 peaks centred above 500 K, indicating associative desorption of O2 from Ag metal surface sites. By varying the heating rates from 2 to 20 K min-1, the O2 TPD peak maxima were found to shift from 508 to 542 K, respectively. A microkinetic analysis of these TPD traces yielded an activation energy for desorption of 149±2 kJ mol-1 and a corresponding pre-exponential factor of 2×1012±1×1012 s-1 in good agreement with the kinetic parameters reported for O2 desorption under UHV conditions from Ag(111) and Ag(110) single crystal surfaces.