Dynamics of oxygen and hydrogen species at the surface Ru/Al 2 O 3 revealed by advanced operando spectroscopies

The microscopic evolution of supported Ru-oxide nanoparticles under reducing conditions remains a central challenge in hydrogenation catalysis. In 5 wt% Ru/Al2O3 catalyst, the transformation of oxidized Ru species into metallic Ru, the formation of hydrides, and hydrogen exchange with the support are closely related but difficult to resolve simultaneously. Here, operando IR and O K-edge NEXAFS, supported by quantum chemical DFT calculations, show that the initially hydroxylated Ru-oxide surface contains *OOH and *OO-H species at unsaturated Ru sites characterized by a distinct O K-edge electronic signature. Upon dehydration, removal of neighboring surface groups strongly stabilizes a bridged η2-peroxo species with a characteristic vibrational fingerprint. Subsequent exposure to H2 drives a low-temperature multistep reduction to metallic Ru and leads to the transient formation of terminal Ru–H species. Inelastic neutron scattering (INS) measurements independently reveal multi-coordinated hydrides under hydrogen-rich conditions, while H/D isotope exchange shows reversible hydrogen exchange between Ru nanoparticles and the support. The concomitant recovery of alumina hydroxyl groups upon H2 exposure further supports hydrogen transfer to the support. These results provide insight on the evolution of the catalyst, showing that surface dehydroxylation, Ru-oxide reduction, hydride formation, and hydrogen transfer are closely connected during activation of Ru/Al2O3 catalysts.