Vanadium trichloride (VCl3) is one of the best catalysts for the hydrogenation dehydrogenation Mg-MgH2 system. X-ray photoelectron spectroscopy (XPS) has shown that VCl3 reduced to metallic vanadium during ball milling along with MgH2. The in -situ formed metallic vanadium doped over the MgH2 surface which has shown an excellent catalytic effect on hydrogenation-dehydrogenation of the Mg MgH2 system. The catalyzed surface reduced the activation energies of hydrogenation-dehydrogenation reactions and correspondingly on-set hydrogenation-dehydrogenation temperatures. The microstructural analysis has also shown an excellent grain refinement property of VCl3 which reduced the crystallite size of MgH2. The decreased crystallite size decreases the diffusion path length of hydrogen and increases the active surface area which eventually enhances the hydrogenation-dehydrogenation kinetics of Mg MgH2. (C) 2018 Hydrogen Energy Publications LLC. Published by Elsevier Ltd. All rights reserved.