Mg nanoparticles (NPs) with addition of Ti catalysts were synthesised by inert gas condensation and in situ hydrogenation at 150 °C. The NPs size and composition were systematically investigated by scanning electron microscopy, energy dispersive X-ray spectroscopy and powder X-ray diffraction (PXD), while time resolved in situ synchrotron radiation-PXD was used to monitor the mechanism for hydrogen uptake and release at 280 °C. The Mg–Ti NPs reveal activation energies of 68 kJ mol−1 for absorption and 78 kJ mol−1 for desorption by isothermal kinetics analysis, similar to the lowest values reported in the literature for MgH2 using Nb2O5 as a catalyst. Hence, hydrogen desorption (pdes = 8 mbar) and absorption (pabs = 260 mbar) is achieved at 200 °C in ∼2000 s, while keeping 5.3 wt% storage capacity. Thermodynamic data extracted from van ’t Hoff plots reveal unchanged values compared to bulk MgH …