A mechanistic study of hydrogen spillover in MoO(3) and carbon-based graphitic materials.

We present a systematic study of the mechanisms of the hydrogen spillover process from a Pt(6) cluster onto a well-known hydrogen bronze material, MoO(3), and several carbon-based materials, including a graphene sheet and single walled carbon nanotubes, using density functional theory (DFT). We show that initially hydrogen undergoes a sequential dissociative chemisorption upon interacting with the Pt(6) cluster. The threshold desorption energy of H atoms was identified. We then mapped out the energetics required for hydrogen atoms to flow onto the surfaces of the selected materials in the vicinity of the subnanometer Pt(6) particle and to diffuse to other sites of the substrates. Our results indicate that while the spillover of H atoms onto the MoO(3) lattice can be greatly facilitated by the abundant H-bonding network, the process becomes energetically difficult on carbon-based materials via chemisorption since it requires C-H bond breaking. Spillover in the selected carbon-based materials could only become possible if 'cold' H atoms could come out of the saturated catalyst.