Coal gasification processes, such as the Integrated Gasification Combined Cycle (IGCC), will increase in importance due to the expanding concern over CO2 emissions and global climate change. During the development of a Pd/gamma-Al2O3 sorbent for warm (200 degrees C) fuel gas cleanup, the catalytic formation of carbonyl sulfide (COS), was observed. This is attributed to a heterogeneous reaction involving fuel gas components (CO/CO2/H-2/H2S/H2O) and Pd/gamma-Al2O3. The concentration of COS increases 200-fold when exposed to the Pd/gamma-Al2O3 sorbent. A Langmuir-Hinshelwood reaction mechanism is proposed and a kinetic model is developed based on experimental results. The effect of gamma-Al2O3, a common catalyst for hydrolysis of COS, and H2O on the COS concentration is discussed. Published by Elsevier Ltd.