A comparative study of the hydrogen spillover phenomenon on pristine graphene and anatase (101)-supported Pt 4 catalysts has been carried out by using density functional theory with Hubbard correction (DFT + U) and dispersion correction (Grimme-D3). The adsorption of the H 2 molecule causes no dissociation on graphene but dissociation with nearly zero adsorption energy on anatase (101). This emphasizes the need for a metal catalyst for H 2 dissociation to aid the stronger chemisorption of hydrogen atoms or protons on the substrate. The metal−support interaction is different for both substrates as Pt 4 shows p-type doping for graphene and n-type doping for anatase (101) surfaces with binding energies of −2.16 and −5.82 eV, respectively. The differing nature of H 2 adsorption and metal−support interactions lead to different hydrogen spillover phenomena for the two supports. Hydrogen spillover is unlikely to occur on Pt 4 /graphene even at high hydrogen coverage (24H atoms per Pt 4 ) but has a tendency to take place on anatase (101) at medium hydrogen coverage (10H atoms per Pt 4 ) from the perspectives of both thermodynamics and kinetics.