Heterostructured CeO-M (M = Co, Cu, Mn, Fe, Ni) Oxide Nanocatalysts for the Visible-Light Photooxidation of Pinene to Aroma Oxygenates.

Herein, we report the enhanced photocatalytic activity of heterostructured CeO nanocatalysts interfaced with Cu, Co, Ni, Mn, and Fe metal oxides. The CeO catalysts exhibited an enhanced red shift in the visible-light response compared to CeO. This improved absorption range effectively suppressed electron (e)/hole (h) recombination by forming localized energy bands associated with defect oxygen vacancies ( ) induced by the M ions incorporated in CeO. Under visible-light irradiation, CeO catalysts are active for α-pinene oxidation to the aroma oxygenates, pinene oxide, verbenol, and verbenone. Both FeO-CeO and NiO-CeO gave the highest pinene conversions of 71.3 and 53.1%, respectively, with corresponding pinene oxide selectivities of 57.3 and 58.2%. The enhanced photocatalytic performance of the heterostructured CeO catalysts compared to CeO is attributed to their enhanced visible-light absorption range and efficient suppression of e/h recombination. The FeO-CeO catalyst was highly recyclable and did not show any significant loss of its photoactivity.