While it is not abundantly clear whether the HEB of Al0.2Nb0.2Pt0.2Ta 0.2Ti0.2B2 uses the hydrogen spillover effect (HSPE) or the hydrogen atom transfer (HAT) mechanisms as a catalyst in hydrogenation reactions. Some valuable insights have been obtained from the work done here; for example, it is critical that the HEB is synthesized using a flux growth method, this is pivotal for obtaining clear facets along the crystals, allowing abundant room for platinum to perform the catalysis within the diboride. The heterogeneous hydrogenation reactions of both WO3 and TEMPO and comparing their successful reactions between the HEB and pure platinum catalyst without a support suggests that the mechanism for the HEB hydrogenation catalysis goes through a hybrid HAT/HSPE mechanism. We propose that the mechanism for hydrogenation is a hybrid of the two, where the H2 bonds to the platinum atoms on the facet edges of the HEB, dissociates, and then the radical hydrogens will depart to the substrate.