Additive-Free, Selective Synthesis of N -Heteroaromatics Using Morphology-Engineered Hollow CeO 2 Nanocatalyst

We developed a highly efficient, shape-controlled CeO 2 nanocatalyst for synthesizing N -heteroaromatics via an aerobic dehydrogenation approach, operating at mild reaction conditions without needing toxic acid/base additives. Different morphologies of CeO 2, namely, hollow nanospheres, nanorods, and irregularly shaped nanoparticles, were synthesized, as confirmed by electron microscopy analysis. The CeO 2 hollow nanosphere catalyst (CeO 2 –HNS) exhibited unique features, such as abundant acid–base sites, larger-sized voids, and surface oxygen vacancies. These characteristics are found to be crucial for the additive-free oxidative dehydrogenation of saturated N -heterocycles over the CeO 2 –HNS catalyst, resulting in 98% conversion of 1,2,3,4-tetrahydroquinoline with 100% quinoline product selectivity. The versatility of this approach was further demonstrated by the successful aerobic dehydrogenation of a broad range of saturated N -heterocycles, affording N -heteroaromatics in good to excellent yields. Furthermore, the CeO 2 –HNS nanocatalyst showed exceptional reusability over six cycles without requiring a regeneration step, such as high-temperature calcination treatment. The structural and morphological stability of the CeO 2 –HNS catalyst, along with reaction scalability and favorable green chemistry metrics, emphasized the practical viability of the CeO 2 –HNS catalyst for industrial applications.