Activated carbon fiber-phenolic resin composite, which has a form of honeycomb monoliths, has been used to capture CO2. A theoretical model was proposed and utilized to predict the sample's breakthrough curves under various structural conditions to study the relationship between the sample's monolithic structure and its adsorption performance. Three geometric factors including number of channels, internal channel diameter and sample's diameter were chosen to vary while the sample's weight was kept constant. It is found that the sample's adsorption performance increases proportionally with the increase of its void fraction. The sample with thinner channel walls also achieves better adsorption performance. As far as the optimal structure is concerned, the effect of the sample's diameter is considered negligible as long as the void fraction is maintained. By increasing either the number of channels or internal channel diameter, the sample's adsorption performance can be improved. However, a smaller channel size is preferred due to its potential in reducing the sample size. More channels thus have to be made to achieve a certain void fraction. (C) 2011 Elsevier Ltd. All rights reserved.