Regularities in the temperature-programmed desorption spectra of CO2 and CO from activated carbons

Temperature-programmed desorption (TPD) spectra of CO and CO2 have been obtained under vacuum or helium flow with activated carbons from different origins and oxidized in various ways. In particular, a special form of TPD, called Intermittent TPD, has been applied to one of the carbon samples (prepared from almond shells and oxidized with nitric acid) in order determine the variation of the apparent activation energy of desorption Ed as the coverage of the surface decreases. Regularities appeared in the set of results obtained: There are common features in TPD profiles of carbons from different origins and histories. This finding is confirmed by a re-examination of numerous CO and CO2 spectra found in the literature, including results obtained under ultra-vacuum. These regularities are interpreted by the existence of the same superficial entities (various oxygen groups with different environments). (C) 2000 Elsevier Science Ltd. All rights reserved.