Metal nanoparticles such as Ni, Cu, and Co were prepared within polyethyleneimine (PEI) microgels and were used in the reduction of 4-nitrophenol (4-NP) and 2-nitrophenol (2-NP) to 4-aminophenol (4-AP) and 2-aminophenol (2-AP). The metal nanoparticle content of the prepared PEI-M composite catalyst system (M=Co, Ni, and Cu) was increased by multiple loading and reduction cycles into PEI microgels to provide faster and better reduction of 4-NP and 2-NP. The TOF value increased to 1.48 from 0.353 (mol 4-NP (mol catalyst min)(-1)) for 4-NP reduction catalyzed by PEI-Ni after three cycles of metal loading and reduction. The effect of temperature on 4-NP and 2-NP reductions catalyzed by PEI-M illustrated that higher temperature resulted in very fast reductions, e.g., at 70 degrees C 4-NP and 2-NP reduction by PEI-Ni resulted in very fast reduction times of 1.2 and 0.67 min to 4-AP and 2-AP, respectively. The activation parameters, such as energy, entropy, and enthalpy, were also calculated and mild activation energies of 38.8 and 46.0 kJ mol(-1) for 4-NP and 2-NP catalyzed by PEI-Ni were found, respectively, in comparison to similar studies in the literature. Moreover, it was demonstrated that PEI-Ni microgels are reusable five times consecutively, with almost 100 % conversion and 100 % of their catalytic activity.