Core-shell zirconia-coated magnetic nanoparticles offering a strong option to prepare a novel and magnetized heteropolyacid based heterogeneous nanocatalyst for three- and four-component reactions

A new type of magnetically-separable nanocatalyst was prepared through the immobilization of phosphomolybdic acid (H3PMo12O40) in 10–30wt.% on the surface of core-shell zirconia-coated magnetite nanoparticle (nano-Fe3O4@ZrO2). The developed heterogeneous nano-sized acid catalyst named nano-Fe3O4@ZrO2 supported PMA (or n-Fe3O4@ZrO2/PMA) was characterized using several techniques such as FT-IR, XRD, FE-SEM, VSM, EDX, TEM and TGA. The characterization data derived from FT-IR spectroscopy exhibited that H3PMo12O40 species on the support retained their Keggin structures. Additionally, the potentiometric titration with n-butylamine was employed to measure the acidity content of the as-obtained catalyst. Surprisingly, this novel active solid acid catalyst displayed to have a higher number of surface active sites compared to its homogeneous analogues. Besides, the catalytic activity of the catalyst was evaluated in multicomponent reactions (MRCs) for the rapid and efficient one-pot synthesis of 2, 4, 5-trisubstituted and 1, 2, 4, 5-tetrasubstituted imidazoles in high yields and selectivity. The sample of 20wt.% displayed higher acidity content which led to its enhanced activity in the catalytic transformation. Moreover, the catalyst could be easily reused without deactivation after five runs, which made it a promising catalyst for practical and large-scale applications. This outstanding reusability was ascribed to the strong attachment of PMA molecules on the n-Fe3O4@ZrO2 support material.