The solar thermo-catalytic decomposition of methane over carbonaceous catalysts was studied as an attractive process for CO2-free hydrogen production using solar concentrated energy as the high-temperature process heat source. The reaction produces pure hydrogen and carbon as a co-product formed on the catalyst surface. The work was devoted to gravimetric solar tests using an in-house made solar-driven thermogravimetric device designed for investigating the reaction kinetics. The study aims to measure the mass variation of the carbon catalyst with time during methane decomposition due to carbon deposition. The catalytic activity of different types of carbon (carbon black as powder or pellets, activated charcoal) can be compared, and the deactivation kinetics can then be investigated as a function of the operating parameters. Both the initial reaction rate of methane decomposition and the long-term catalyst behavior defined by the capacity to accumulate carbon before deactivation were assessed. The carbon black powders remained active after a long period of methane decomposition at 1000 degrees C or 1100 degrees C in contrast to pellets, while activated carbon showed higher initial catalytic activity followed by fast deactivation in comparison with carbon black. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.