Nanoceria as an Efficient and Cost-Effective Metal-Free Catalyst for the Oxidation of Alcohols

This study investigates the catalytic properties of nanoceria for the liquid-phase oxidation of aromatic and aliphatic alcohols using <i>t</i>-butyl hydroperoxide as an oxidant without the need for base or supported noble metals. The morphology, reducibility, and reversible H₂ adsorption characteristics of ceria were comprehensively studied using X-ray diffraction, BET, HAADF-STEM, H₂-TPR, H₂-TPD, and X-ray photoelectron spectroscopy. Radical formation was interrogated by electron paramagnetic resonance (EPR) using dimethyl pyrrolidine <i>N</i>-oxide (DMPO) and <i>N</i>-<i>tert</i>-butyl-α-phenylnitrone (PBN) as spin traps, complemented by atomistic simulations to elucidate the influence of trap and radical adduct adsorption on the catalysts on radical abundance. The solvent played a critical role in enhancing the catalytic performance and carbon balance. The catalyst retained its structural integrity during the reaction in acetonitrile and could be reused for at least five consecutive runs. EPR analysis revealed that peroxyl radicals (<i>t</i>Bu-OO^•) were the predominant reactive species with no detectable formation of oxyl (<i>t</i>Bu-O^•) radicals, ruling out a Fenton-like catalytic mechanism in solution. Incorporating small amounts of Au (0.5-1.0 wt %) as Au-(I) single atoms or clusters reduced the catalytic activity due to a decreased surface reducibility and reversible H₂ adsorption despite an increased peroxyl radical formation. However, Au doping did not alter the product distribution. Compared to a benchmark 0.3 wt % Au/TS-1 catalyst, nanoceria achieved a 60% cost reduction and an <i>E</i>-factor of 0.08 (vs 0.2-1.3 for 0.3 wt % Au/TS-1) at equivalent acid production rates, highlighting the economic and environmental benefits.