DFT calculations for SO4/graphene with and without a Pd atom

We investigated the adsorption of SO4 on graphene surfaces, and Pd on the adsorbed SO4 on graphene, by using first-principles calculations based on the density-functional theory. Three stable configurations were found for SO4/graphene, in which three O atoms in the SO4 molecule bond to the graphene surface. The adsorption energies of SO4 onto graphene and that of Pd&SO4 onto graphene are 1.61 eV and 0.38 eV, respectively. A Pd atom added binds chemically to two O atoms of SO4. The stable position of Pd is between two O atoms and on top of the bridge site between two C atoms of graphene. The O–C bond length near Pd is longer than that in SO4/graphene without Pd because of the hybridization of the Pd orbital and the O orbital. This means that the C–O bond may be dissociated when Pd is present. Our results are highly valuable for experimentalists using graphene as a catalyst substrate.