Formaldehyde as a Hydrogen Shuttle: Redefining Spillover Pathways on Nonreducible Oxide Surfaces

Hydrogen spillover on nonreducible oxides such as SiO2 is often inefficient because, unlike reducible oxides, their inert surfaces are less capable of stabilizing and transporting migrating hydrogen species. Here, we identify formaldehyde (HCHO) as an efficient hydrogen shuttle on hydroxylated SiO2-supported Pt (Pt/SiO2-OH), where it mediates H transfer through reversible sp2-sp3 hybridization switching at its carbon center. Using density functional theory and ab initio molecular dynamics simulations, we show that HCHO-assisted H relay proceeds through two spatially distinct modes. Near the Pt cluster, HCHO captures a hydrogen atom and forms a surface-anchored hydrogenated intermediate, which transfers H to a neighboring HCHO molecule through rotational reorientation. Far from the cluster, where the downshifted O 2p-band center weakens the anchoring, the hydrogenated species adopts a floating mode, enabling sustained transport across the inert surface. This transition from an anchored relay to a floating relay, in which weakened surface anchoring becomes a functional advantage, provides a mechanistic basis for sustained HCHO-mediated H relay on SiO2-OH.