The reserves of fossil energy sources can meet the global energy demands for years to come, but their utilisation is constrained by environmental considerations. Hydrogen can be generated from fossil fuels like methane without CO2 emissions by pyrolysis at temperatures above 600 degrees C. In the fluid wall flow reactor concept, the heating gas is introduced through a porous reactor wall. Using a ceramic membrane with 3 um pore diameter and helium as heating gas proved the best choice for long-term experimentation. The influence of methane diffusion into the outer heating chamber was studied and explains the decrease in conversion from 53% to 7% over 7 h, after which the conversion remains low but constant. The slug flow of methane and molten metal in a capillary enables one to extend the pyrolysis residence time and, if the molten metal forms a contiguous thin liquid film on the capillary wall, to avoid problems with carbon deposition and reverse reaction. The studies presented, using a 2 mm ID quartz glass capillary with molten tin and nitrogen and a superficial velocity of 0.092 m s(-1), demonstrate that the use of molten metal in the capillary reactor is both controllable and feasible. Initial experiments with methane at 1100 degrees C and a superficial velocity of 0.122 m s(-1) show that methane can be decomposed with an average conversion of 32% and without carbon depositions. Copyright (C) 2015, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.