Hollow CeO₂ Nanospheres as Catalyst for the Conversion of Aromatic Diamines to Benzimidazoles

Utilization of anthropogenic CO₂ for the synthesis of valuable heterocyclic compounds is a very significant strategy to alleviate environmental issues. Herein, a hollow CeO₂ nanosphere (HNS–CeO₂) material made using solvothermal-method-assisted synthesis was employed as an efficient catalyst for the selective benzimidazole synthesis under neat and temperate reaction conditions. We examined the controlled reaction conditions for the design of the HNS–CeO₂ material through the study of various reaction parameters. Very interestingly, the HNS–CeO₂ material exhibited different surface morphological disparities due to the effect of various reaction parameters that were examined comprehensively using field emission scanning electron microscopy analysis. The HNS–CeO₂ material was systematically well characterized using various analytical and spectroscopic techniques. The competent catalyst of HNS–CeO₂ showed superior catalytic activity (100% conversion, 96% selectivity, and yield) under mild reaction conditions, and these conditions are successfully identified by studying the effect of various reaction parameters. Remarkably, the inherent properties of the HNS–CeO₂ catalyst boosted the synergistic effect with the model reagents of o-phenylenediamine, carbon dioxide, dimethylamine borane (DMAB), and base. Moreover, different functional groups substituted benzimidazole compounds are successfully synthesized in good to excellent yields under optimized reaction conditions. The effective contributions of DMAB, base, Lewis acidic, and Lewis basic sites were successfully revealed by proposing a tentative benzimidazole reaction mechanism. Notably, the examined 15 successive recycles with stable catalytic activity performance demonstrated the stable catalytic activity and structural and physicochemical properties of the HNS–CeO₂ catalyst.