Polyacrylonitrile (PAN)-based carbon fibers (CFs) have been activated by steam treatments, then used as a catalyst support. The changes in microporous structure and surface chemistry were analyzed. The steam treatment increased significantly the surface area and the number of functional groups of carbon fibers; these factors are responsible for the capacity of ion exchange. Sodium ion-exchanged activated-carbon fiber (ACF) catalysts were studied for the propionitrile (PN) synthesis from methanol and acetonitrile. BET, X-ray diffraction (XRD), TPD, and flame photometry have been applied to characterize the catalysts. The activities of catalysts depend on the sodium content of the carbon fibers, which corresponds to the amount of base on the surface, and on the adsorption capacities of reactants. Sulfur treatment of the ACFs can stabilize the exchanged Na, and therefore the catalyst decay can be reduced. (C) 2003 Elsevier B.V. All rights reserved.