In this work, the effect of powder bed size on the absorption and desorption kinetics of NaAlH(4) catalyzed with TiCl(4) was studied experimentally. For this purpose, volumetric titration measurements were performed using cells of different diameters. The temperature was measured during the process at different positions inside the hydride bed, providing detailed information about the influence of heat conduction. Experimental results show that, under the applied conditions up to a critical size, larger diameters can lead to faster kinetics for the first and second absorption reactions. At larger cell diameters, however, temperatures up to 200 degrees C were measured during the first absorption step in the hydride bed. This leads to a significant delay in the start of the second absorption step, reducing the overall rate of the process. Reasons for the observed behaviour are discussed and measures for optimization are proposed. (c) 2008 International Association for Hydrogen Energy. Published by Elsevier Ltd. All rights reserved.