Structural effects of nitrogen-doped titanium oxide supports on stabilization of ruthenium active species in carbon dioxide hydrogenation to formate

A single atom Ru catalyst supported on a N-doped TiO2 was investigated for the conversion of CO2 to formate by hydrogenation. N-dopant sites induced a strong binding environment to Ru single-atom catalysts (SACs), resulting in a stable and atomically isolated dispersion state of Ru SACs upon metalation. Consequently, Ru/MN-TiO2 exhibited enhanced catalytic stability, which incorporated both substitutional (Ns) and interstitial (Ni) dopant sites, retaining 42 % of its original relative activity after the fifth recycle test. In contrast, Ru/N-TiO2, which contained only Ni-dopants, showed a lower stability, retaining only 19 % of its initial activity after the fifth run, and Ru/TiO2 was fully deactivated after the third run. Density functional theory calculations revealed that the stronger binding ability of the Ns sites to the Ru species compared with that of the Ni sites and the bare surface of the TiO2 structure improved the catalytic stability during hydrogenation.