Ce Decoration-Enhanced Singlet Oxygen Generation of Titanium-Oxide Clusters for Photocatalytic Oxidation of Aromatic Alcohols

In photocatalysis, the nature of reactive oxygen species plays a pivotal role in determining product selectivity. Yet, selective generation of singlet oxygen (¹O₂) is particularly desirable for achieving targeted photooxidations. Herein, two new nanosized titanium-oxide clusters (TOCs) doped with Ce, Ti₁₄Ce₂ and Ti₄Ce₂, were synthesized and explored in the selective photocatalytic oxidation of benzyl alcohols to benzaldehydes under mild conditions. Interestingly, the titanium-oxide core of Ti₁₄Ce₂ is recognized as a fragment of anatase TiO₂, positioning Ti₁₄Ce₂ as a molecular model for Ce-doped TiO₂ nanoparticles. Ce-doping effectively reduces the bandgap energy of the clusters, enabling visible-light absorption and enhancing their photocatalytic properties. Moreover, it promotes efficient energy transfer to O₂ for ¹O₂ generation by increasing spin-orbit coupling. Both clusters exhibited high activity and selectivity in the oxidation of benzyl alcohols to benzaldehydes under visible-light irradiation. Our findings not only expand the TOC family with novel Ce-doped members but also offer insights into designing photocatalysts at the atomic level to enhance ¹O₂ generation for selective photo-oxidations.