Designing well-organized and efficient nanoporous catalysts to enhance the efficiency of catalytic processes is a very intriguing and challenging area. In this study, a metal–organic framework (MOF) based on a novel porous nanocatalyst was prepared via a multistep post-synthetic modification approach. Initially, the Cr-MIL-101-NH₂ was modified with cyanuric chloride and then melamine. Next, the modified MOF was used as the support for the immobilization of cobalt(II) ions by available functional groups, including amino and π–interactions of melamine and ligand on the surface of the modified MIL-101-NH₂, to generate the MIL-101-NH₂-CC/melamine@Co²⁺ catalyst. The structure and morphology of the catalyst were characterized using powder XRD, FTIR, FE-SEM, EDX, elemental mapping, TGA, and N₂ adsorption–desorption isotherm analysis. The catalytic performance of MIL-101-NH₂-CC/Melamine@Co²⁺ was evaluated by one-pot synthesis of 2,4,5-trisubstituted imidazole derivatives according to Debus–Radziszewski reaction from different aldehydes, benzil, and ammonium acetate under solvent-free conditions. Moreover, the MIL-101-NH₂-CC/Melamine@Co²⁺ catalyst demonstrated significant catalytic activity in the methylene blue dye reduction, with a reduction time of 14 min and a rate constant (k₁) of 0.0141 min⁻¹. The catalyst was recycled and reused five and eight times in synthesizing 2,4,5-trisubstituted imidazole and the reduction reaction with appropriate catalytic activity.