Mg-Al thin films with a compositional gradient are co-sputtered from off-centered magnetron sources and capped with a thin Pd layer. We study their hydride formation by monitoring their optical transmission during hydrogenation under defined pressure and temperature conditions. We find that Mg(AlH 4)2 is already formed from the elements at p(H2)=1 bar and T=100 ° C. A thin layer of Ti acts as a catalyst. Doping of Mg-Al with Ti has a negative influence on hydrogen absorption.