Intermittent temperature-programmed desorption of ammonia was used to study the strength and population of surface acid sites of tungsten oxide supported on activated carbon pretreated at 350 and 700 degreesC. Catalysts pretreated at 350 degreesC showed two types of surface acid sites and desorption occurred with free readsorption until a temperature of around 300 degreesC was reached. Pretreatment at 700 degreesC produced three different states of ammonia adsorbed on the catalysts and desorption occurred with free readsorption. (C) 2003 Elsevier Science (USA). All rights reserved.