Deactivation of 0.5 wt.% Pt/gamma -Al2O3 catalysts during trichloroethylene (TCE)-steam reforming was studied with experiments at 700 degreesC, H2O/C = 25 and GHSV = 60,000 h(-1). Coke deposits at various process times and operating conditions were analyzed with temperature programmed oxidation to determine total carbon deposition and WC ratios. Total chlorine adsorption was also determined by chemical analysis, and the chlorinated surface examined with X-ray photon spectroscopy. The effect of process time and environment on the platinum dispersion was measured with hydrogen chemisorption and the gamma -Al2O3 surface area determined with BET studies. Finally, the crystallite size of the platinum and phase transformations of the gamma -Al2O3 support were found from X-ray diffraction. These studies indicated that the major source of permanent deactivation is loss of platinum surface area due to crystallite sintering and encapsulation caused by phase transition in the support. Chlorine poisoning decreases the water gas shift activity but not the main reaction. However, chlorine saturation of the surface deters steam from removing carbon and maintaining a clean catalyst. Coke formation only becomes significant as these other factors enlarge the reaction zone and provide the opportunity for pyrolysis and hydrogenolysis reactions to occur within the pores.