AbstractA reactive hydride composite (RHC) with initial composition 3CaH2 + 4MgB2 + CaF2 was studied by in situ synchrotron radiation powder X-ray diffraction (SR-PXD) and X-ray absorption near edge structure (XANES) at the B K-edge and at the Ca K-edge. The hydrogenation reaction proceeds by an unknown intermediate. No evidence of intermediates was observed during the dehydrogenation reaction. B and Ca K-edge XANES results hint to a closed interaction of CaF2 and Ca(BH4)2. The main function of CaF2 in the 3CaH2 + 4MgB2 + CaF2 RHC is as a dopant for the hydrogenation and dehydrogenation reactions.