Palladium hydride and deuteride are known for more than 100 years and have been well investigated. Structural data at non ambient conditions, however, are scarce, real-time studies not available. We would therefore like to use our recently developed single crystal based sapphire gas pressure cell to investigate the hydrogenation as well as the deuteration of palladium. Both reactions shall be followed through the two-phase region, where alpha and beta palladium hydride (deuteride) coexist, and at higher temperatures above the critical point. These investigations will yield new structural data at non ambient conditions not available before, allow to link these structure data to the kinetics observed in these real time studies and to test the hypothesis of tetrahedral void occupancy of deuterium in the supercritical region of the phase diagram.