Both
noble metals and transition metal oxides are recognized as
active centers for alkyne hydrogenation. However, it is still a “black
box” how the catalytic behavior of oxides evolves upon the
catalytic intervention of noble metals. Herein, we report a modularized
strategy to track the hydrogenation mechanism of oxides (e.g., TiO2, CeO2, and ZrO2) using a core–shell
micromesoporous zeolite as a structure model, in which the oxide and
noble metal (Pt) are functionally separated within a mesopore shell
and a micropore core (TS-1 zeolite), respectively. The Pt species
are atomically distributed and stabilized by the oxygen atoms of five-membered
rings in TS-1 zeolite, which facilitates the heterolytic activation
of dihydrogen over Ptδ+···O2– units. The active hydrogen species, i.e., H+ and Hδ−, migrate to the oxide surface, where the adsorbed
reactants are activated for hydrogenation. Mechanistic studies reveal
that TiO2, CeO2, and ZrO2 possess
efficient hydrogenation properties at near-room temperature with the
assistance of spillover hydrogen species, demonstrating dihydrogen
dissociation as the main rate-limiting step for pure oxide. Impressively,
the adsorbed H2O molecule on TiO2, ZrO2, and CeO2 not only acts as a bridge of hydrogen spillover
in reducing the proton diffusion barrier but also forms H3O+ species on the TiO2 (100) surface and endows
TiO2 with extraordinary hydrogenation properties. This
work opens the “black box” for the hydrogenation behavior
of transition metal oxides and develops a molecule-assisted strategy
for the rational design of hydrogenation catalysts.