Heterostructured CeO2-M (M = Co, Cu, Mn, Fe, Ni) Oxide Nanocatalysts for the Visible-Light Photooxidation of Pinene to Aroma Oxygenates

Mlungisi A Mavuso; Peter R Makgwane; Suprakas Sinha Ray

doi:10.1021/acsomega.9b04396

Heterostructured CeO₂-M (M = Co, Cu, Mn, Fe, Ni) Oxide Nanocatalysts for the Visible-Light Photooxidation of Pinene to Aroma Oxygenates

ACS Omega. 2020 Apr 23;5(17):9775-9788. doi: 10.1021/acsomega.9b04396. eCollection 2020 May 5.

Authors

Mlungisi A Mavuso¹, Peter R Makgwane^{2

3}, Suprakas Sinha Ray^{1

2}

Affiliations

¹ Department of Chemical Sciences, University of Johannesburg, Doornfontein, 2028 Johannesburg, South Africa.
² Centre for Nanostructures and Advanced Materials, Council for Scientific and Industrial Research (CSIR), Pretoria 0001, South Africa.
³ Department of Chemistry, University of the Western Cape, Bag X17, Robert Sobukwe Drive, Bellville 7535, South Africa.

Abstract

Herein, we report the enhanced photocatalytic activity of heterostructured CeO₂ nanocatalysts interfaced with Cu, Co, Ni, Mn, and Fe metal oxides. The CeO₂ catalysts exhibited an enhanced red shift in the visible-light response compared to CeO₂. This improved absorption range effectively suppressed electron (e^-)/hole (⁺h) recombination by forming localized energy bands associated with defect oxygen vacancies (V _o) induced by the Mⁿ⁺ ions incorporated in CeO₂. Under visible-light irradiation, CeO₂ catalysts are active for α-pinene oxidation to the aroma oxygenates, pinene oxide, verbenol, and verbenone. Both Fe₂O₃-CeO₂ and NiO-CeO₂ 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 CeO₂ catalysts compared to CeO₂ is attributed to their enhanced visible-light absorption range and efficient suppression of e^-/⁺h recombination. The Fe₂O₃-CeO₂ catalyst was highly recyclable and did not show any significant loss of its photoactivity.