Dynamic adsorption of ammonia on activated carbons measured by flow microcalorimetry

Several activated carbons of different textural and chemical surface characteristics have been used to study the ammonia adsorption. The textural characteristics were determined by N-2 and CO2 adsorption at 77 and 273 K. The chemical surface groups were estimated by thermal programmed desorption followed by mass spectrometry (TPD-MS) and by selective titrations in aqueous solutions, The ammonia adsorption was studied under dynamic conditions from N2 diluted flow using a flow adsorption microcalorimeter. The ammonia adsorption consists of reversible and irreversible components. The former is assigned to physisorption process while the latter is adsorption on chemical groups. The plots of the differential heats of adsorption versus the cumulative adsorption point to the existence of a wide distribution of acid sites some of which are very strong. However, they are not always easily accessible to NH3 because constrictions in the pores-network hinder the access which forces to re-arrangement. (C) 2002 Elsevier Science B.V. All rights reserved.