Redox-active cobalt substituted manganese spinel ferrite as recyclable catalyst for multicomponent heterocyclic synthesis

Abstract

Cobalt-substituted manganese ferrites with the general formula Mn sub(1-x)Co sub(x)Fe sub(2)O sub(4) (x = 0.2, 0.4, 0.6, 0.8) previously prepared via auto-combustion method were characterized using Raman spectroscopy, Brunauer-Emmett-Teller (BET) surface area analysis, and X-ray photoelectron spectroscopy (XPS) to elucidate their structural, textural, and electronic features. In addition, NH sub(3) temperature-programmed desorption (TPD) studies were performed to evaluate the strength and distribution of acidic surface sites. Raman spectroscopy confirmed the retention of the spinel structure and revealed vibrational features sensitive to cationic redistribution. BET analysis indicated mesoporous characteristics with Mn sub(0.4)Co sub(0.6)Fe sub(2)O sub(4) exhibiting the highest surface area (27.59 m sup(2)/g) and optimal pore volume, correlating with superior catalytic performance. NH sub(3-)TPD studies revealed the dominance of medium-strength acid sites in this composition, which facilitate substrate activation and intermediate stabilization. The trend observed from BET surface area and NH sub(3-)TPD acidity measurements - Mn sub(0.4)Co sub(0.6)Fe sub(2)O sub(4) greter than Mn sub(0.8)Co sub(0.2)Fe sub(2)O sub(4) greater than Mn sub(0.2)Co sub(0.8)Fe sub(2)O sub(4) greater than Mn sub(0.6)Co sub(0.4)Fe sub(2)O sub(4), indicates the importance of cobalt substitution level to be crucial for balanced surface acidity and accessible porosity. Mn sub(0.4)Co sub(0.6)Fe sub(2)O sub(4) was employed for heterogeneous catalysis in the synthesis of biologically relevant heterocycles-dihydropyrimidinones and imidazoles-via Biginelli and Debus-Radziszewski reactions, respectively. The catalyst enabled good to excellent yields under mild and environmentally benign conditions. This study establishes a direct correlation between composition, structure, and catalytic behaviour, demonstrating the potential of cobalt-manganese ferrite as efficient, reusable nanocatalyst for sustainable organic synthesis.