Temperature programmed desorption from LiAlO 2 treated with H 2

Abstract

Temperature programmed desorption (TPD) measurements have been made of H2O and H2 desorption from LiAlO2 treated at 923 K with He-H2 mixtures containing 990, 495, and 247 vppm H2. Desorptions were into sweep gases of pure He and into He-H2 mixtures. The H2O and H2 desorption peaks were shown to be the sums of first order subpeaks which had reproducible desorption activation energy and pre-exponential terms. For H2O desorption, the activation energies were 96, 117, and 134 kJ/mol (23, 28, and 32 kcal/mol). (Earlier work had identified an additional peak with an activation energy of 75 kJ/mol (18 kcal/mol.) Enhancement of desorption of H2O by H2 in the sweep gas was confirmed. The enhancement results not from modifying the activation energies and pre-exponential terms for the various sites but from changes in the populations of sites participating in the desorption process so that sites with lower activation energies are increasingly involved. For those runs with He as the sweep gas, desorption of H2 could be observed. The subpeaks involved had activation energies within approximately 4 kJ/mol (1 kcal/mol) higher than the analogous peaks for H2O desorption.