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

Abstract

Utilization of anthropogenic CO 2 for the synthesis of valuable heterocyclic compounds is a very significant strategy to alleviate environmental issues. Herein, a hollow CeO 2 nanosphere (HNS−CeO 2 ) 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−CeO 2 material through the study of various reaction parameters. Very interestingly, the HNS−CeO 2 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−CeO 2 material was systematically well characterized using various analytical and spectroscopic techniques. The competent catalyst of HNS−CeO 2 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−CeO 2 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−CeO 2 catalyst.

Harnessing the Engineered 2D Triazine-Based Metal-Anchored Covalent–Organic Framework as a Catalyst for Selective Conversion of CO2 into Value-Added Products at Atmospheric Pressure

“…It indicates that there are no Lewis acidic sites functionalized within the COF. Furthermore, the examined Mn@COF profile clearly achieved the Lewis acidic characteristic peaks at 1575 and 1522 cm –1 , indicating that the successfully functionalized Mn 2+ atoms with the N atoms in the COF were evidently detected as having Lewis acidic sites by adsorbing pyridine molecules . Hence, pyridine adsorption analysis and its results evidently exhibited Lewis acidic sites (Mn 2+ ) that are functionalized in the designed Mn@COF catalyst.…”

“…Initially, the FT-IR and pyridine FT-IR (Fourier transform infrared spectroscopy) analyses were recorded by the PerkinElmer FT-IR instrument in transmittance mode (400–4000 cm –1 ) by the known method . The Mn@COF material thermal stability was examined by using a thermal analyzer (STA) 6000 (PerkinElmer) in 100 mL/min nitrogen (N 2 ) flow in the temperature range of RT–800 °C (10 °C/min).…”