A novel approach is presented and explored for porosity characterization an
d the study of porosity development in carbons and chars during activation
processes. This approach involves the interpretation of post-activation tem
perature programmed desorption (TPD) spectra. The procedure involves first
forming oxygen complexes on a carbon surface by oxygen gasification. Subseq
uently, the sample temperature is raised in a low-pressure inert carrier ga
s (helium) at a programmed heating rate, during which the rates of evolutio
n of CO and CO2 are measured. A comparison of gas evolution results and sur
face areas determined from nitrogen adsorption isotherms using the alpha (s
)-plot method, show that there exist strong correlations between the nature
of the resultant porosity and its development, and post-reaction desorptio
n features of oxygen surface complexes formed during the activation process
. It is demonstrated that the surface area of the larger pores and the tota
l CO2 evolved upon TPD are correlated. It is concluded that the GO-evolving
complexes are formed over the entire surface area of the chars during acti
vation, but that the surface area in the larger porosity is primarily respo
nsible for the formation of CO2-evolving surface complexes. The relationshi
p between micropore surface area and the CO evolution 'corrected' for the e
xpected contribution from carboxylic acid anhydride surface complexes in th
e larger porosity, indicates that these latter types of complexes may be re
sponsible for much of the CO2 evolution under conditions when oxygen is the
activating agent. (C) 2001 Elsevier Science B.V. All rights reserved.