Nickel peroxide nanoparticles (NPNPs) were prepared and characterized using various techniques including transmission electron microscope (TEM), scan electron microscope (SEM), energy dispersive spectrometer (EDS), X-ray diffraction (XRD), and FTIR spectra. The aqueous basic catalytic system NiSO4·6H2O/NaOCl/NaOH (pH = 14) was investigated for the catalytic dehydrogenation of benzylamine and parasubstituents to their corresponding nitriles at room temperature. The obtained results confirmed the formation of NiO2 nanocrystalline particles with a size of 20 nm. Benzylamine with electron-donating groups showed higher yields of nitriles compared to electron-withdrawing groups. The mechanism involved in the in situ generated NiO2 nanoparticles dehydrogenating benzylamine to benzonitrile, with the produced NiO converting back to NiO2 nanoparticles through the excess of NaOCl.