Oxidation of SO₂ to SO₃ by Cerium Oxide Cluster Cations Ce₂O₄⁺ and Ce₃O₆⁺

Cerium oxide cationic clusters (CeO₂)_1–3⁺ were generated through laser ablation and then reacted with sulfur dioxide (SO₂) at ambient conditions in an ion trap reactor and those reactions were studied and characterized by combining the art of time-of-flight mass spectrometry (TOF-MS) with density functional theory (DFT) calculations. Molecule association and oxygen atom transfer (OAT) were observed for the CeO₂⁺ and (CeO₂)_2,3⁺ reaction systems, respectively. The mechanistic analysis indicates that the weak Ce–O bond strength associated with the oxygen release capacity of cerium oxide clusters is considered as the key factor to achieve the oxidation of SO₂. To our best knowledge, this research should be the first example to identify the OAT reactivity of metal oxide cluster ions toward sulfur dioxide under thermal collision conditions, and a fundamental understanding of the elementary oxidation of SO₂ to SO₃ is provided.