Elevated temperature cycling studies were performed on two commercial gas atomised Mg spherical powders (average diameter of 26 mu m and 30 mu m) with magnetron sputtered catalysts (chromium, iron, vanadium and stainless steel) applied to their surfaces. At 350 degrees C, the presence of a catalyst promotes faster reaction kinetics with improving capacity until approaching stabilisation by the 90th cycle, e.g. the normalised capacity of V_Mg30 was found to rise from 45.5% to 65.5%. Following determination of activation energies (from Kissinger plots) and microstructural analysis of the post cycled structures a mechanism was proposed for the differing evolutions of the uncoated and coated Mg powders based upon a complex process in which particle sintering competes with particle fragmentation. Catalyst effectiveness varied with temperature, having a negligible impact on hydrogen storage characteristics of the atomised Mg powders following 50 cycles at 400 degrees C and this was mainly associated with the lack of multivalency in the catalysts. (C) 2017 Published by Elsevier Ltd on behalf of Hydrogen Energy Publications LLC.