A dynamic method of titration is used to provide evidence for reactive hydrogen (H*) present in different heteropolycompounds (HPC), This method of titration involves hydrogenation of 2-methylbuta-1,3-diene (isoprene) under helium flow in the absence of gaseous hydrogen and permits to reveal and titrate reactive hydrogen species (H*) that a solid is able to store, The heteropolycompounds are catalytic hydrogen reservoirs with marked diffusion properties for hydrogen species (H*, OH-). The hydrogen reservoir capacity depends on the pretreatment temperature under H-2, which has been shown to correspond to the creation of anionic vacancies in the solid by the loss of H2O. In the conditions in which the incorporation of hydrogen in the solids occurs, in-situ X-ray diffraction analysis under H-2 show shifts, depending on the treatment temperature and corresponding to a lattice expansion attributed mainly to the insertion of hydrogen species of hydridic nature in the anionic vacancies.