The catalytic decomposition ("cracking") of ethane was studied over a Ni/SiO2 catalyst at temperatures ranging between 450 and 650 degrees C. In addition to hydrogen and filamentous carbon, methane is also formed during this process as a by-product. SEM images of the spent catalyst indicate the formation of carbon filaments of approximately 50 nm in diameter, almost identical to the original Ni particle size in the fresh catalyst. Measurements conducted at different temperatures and space velocities suggest that hydrogen is the primary product, while methane is formed in a secondary step, presumably the hydrogenation of surface carbon or CH, fragments. Almost complete initial conversion of ethane is observed at a space velocity of 18 000 mL/g It at temperatures above 500 degrees C. Although the initial yield of hydrogen increases with temperature, the rate of catalyst deactivation also increases at higher temperatures. As a result, the overall amounts of hydrogen produced and ethane converted over the lifetime of the catalyst reach maxima at 500 degrees C. (c) 2005 Published by Elsevier B.V.