Supported nickel metal can be used as a tar-cracking catalyst in the thermal processing of large organics to give H-2. Though porous supports offer the opportunity to disperse a relatively large amount of nickel, catalytic sites within small pores may be inaccessible to large tar molecules. To investigate this, we prepared nickel catalysts supported on gamma-Al2O3 and on SBA-15- and mesocellular-foam-(MCF)-type silicas and studied their catalytic activities in the pyrolytic decomposition of cellulose (RT -> 800 degrees C, partial derivative T/partial derivative t = 40 degrees C/min). A thermogravimetric analyser-mass spectrometer (TG-MS) was used to study the influence of the Ni catalyst and support materials on the H-2 yield and selectivity. The silica-MCF-supported Ni catalyst decreased char residue and enhanced H-2 yield, producing 1.6 and 3.5x the H-2 yield obtained using SBA-15-supported Ni and gamma-Al2O3-supported Ni, respectively. MCF, with ultra-large pores (d similar to 15-50 nm), was thus identified as the most beneficial catalyst support for this application. Copyright (C) 2012, Hydrogen Energy Publications, LLC. Published by Elsevier Ltd. All rights reserved.