Catalytic reduction of nitro-phenolic compounds over Ag, Ni and Co nanoparticles catalysts supported on γ-Al2O3

In this work, 1 wt.%Ag/gamma-Al2O3, 1 wt.%Ni/gamma-Al2O3 and 1 wt.%Co/gamma-Al2O3 supported catalysts have been prepared using impregnation method. Their activities were investigated toward the reduction of the nitro-phenolic compounds (NPCs) (ortho-, metha- and para-nitrophenol, respectively, o-NP, m-NP and p-NP) to their corresponding aminophenol compounds (APCs), in the presence of excess of NaBH4 as a reducing agent. Characterization techniques such as (FTIR), (XRD), (SEM/EDX), (UV-vis), (MES/EDS/TEM) and BET textural analysis showed that the metallic nanoparticles of Ag, Ni and Co were well dispersed on gamma-Al2O3 support. The results demonstrated that the unreduced catalysts (fresh and calcined in air) exhibited a good catalytic activities and stabilities for the reduction of NPCs (> 85%) even after 8 catalytic cycles. The catalytic activity of calcined catalysts at T = 450 degrees C, was in the order of 1 wt.%Ag/gamma-Al2O3 > 1 wt.%Ni/gamma-Al2O3 > 1 wt.%Co/gamma-Al2O3 and that of fresh catalysts in the order of 1 wt.%Ag/gamma-Al2O3 > 1 wt.%Co/gamma-Al2O3 > 1 wt.%Ni/gamma-Al2O3. The kinetics of the reduction of the NPCs isomers were studied at T = 25, 35 and 45 degrees C, and were found to follow the kinetics of pseudo-first order and Arrhenius equation. Their reactivities over each catalyst followed the order of p-NP > o-NP > m-NP, except for calcined 1 wt.%Co/gamma-Al2O3. Based on our results and the literature data, a mechanism of catalytic reduction reaction of NPCs has been proposed.