Effects of the Metal–Support Interaction in Ru/CeO₂ Nanostructures on Active Oxygen Species for HCHO/CO Oxidation

Catalysts comprising Ru supported on CeO2 with different morphologies have been widely investigated in various reactions, and the Ru/CeO2-nanorod catalysts have generally demonstrated higher performance. The strong interaction between Ru and CeO2 nanorods, which is beneficial to oxygen activation, is usually considered to be responsible for the higher oxidation activity of the Ru/CeO2 nanostructures. However, how the metal–support interaction of Ru/CeO2 affects the activation of oxygen species still remains elusive. In this work, we prepared two nanostructures consisting of Ru supported on CeO2 nanorod (NR) and nanocube (NC), and the Ru/CeO2-NR catalyst exhibited higher catalytic activity than Ru/CeO2-NC in the oxidation of formaldehyde (HCHO) and carbon monoxide (CO) at low temperatures. The results of complementary characterization techniques revealed that the interaction between Ru and CeO2-NC is actually stronger than that of Ru/CeO2-NR, and more interestingly, we observed that the different Ru–CeO2 interactions induce distinct active oxygen species responsible for the oxidation reactions over Ru/CeO2-NR and Ru/CeO2-NC. The stronger interaction between Ru and CeO2-NC leads to the activation of lattice oxygen on CeO2-NC and a weakened redox capacity of RuOx species. In contrast, the moderate interaction between Ru and CeO2-NR induces a higher redox capacity of RuOx species but weak activation of lattice oxygen on CeO2-NR. The active RuOx on Ru/CeO2-NR is identified as being responsible for the high activity for HCHO/CO oxidation, while the activated lattice O of CeO2-NC in the Ru–CeO2 interfacial domain is the active species on Ru/CeO2-NC, rather than RuOx, resulting in low activity. These findings on Ru/CeO2 nanostructures provide insight into understanding the metal–support interaction over Ru/CeO2 catalysts