Oxidation of 4-nitrophenol in water over Fe(III), Co(II), and Ni(II) impregnated MCM41 catalysts

BACKGROUND: Nitrophenols are toxic constituents of the effluents of petroleum, textile, dye, iron and steel, foundries, pharmaceutical and electrical manufacturing industries. Aromatic nitro compounds are particularly resistant to normal chemical or biological oxidation making them environmentally persistent. Advanced oxidation using appropriate catalysts mineralize these organics to harmless final products. In this work, MCM41-based catalysts incorporating Fe(III)-, Co(II)- and Ni(II)- cations were used for oxidizing 4-nitrophenol in water under variable conditions of reaction time, pH, mole ratio of the reactant and the oxidant, catalyst load, feed concentration, and temperature. RESULTS: The catalysts prepared were characterized with X-ray diffraction (XRD) spectroscopy, Fourier transform infrared (FTIR) spectroscopy, scanning electron microscopy (SEM), cation exchange capacity (CEC) and atomic absorption spectrometry (AAS) measurements. In typical reaction conditions of temperature 353 K, time 300 min, catalyst load 2 g L-1 and 10(-3) mol L-1 4-nitrophenol, the oxidation was 48.7, 52.2 and 55.2% with H2O2 and 42.5, 56.6 and 60.2% without H2O2 for Fe(III)-, Co(II)- and Ni(II)-MCM41, respectively. Pseudo-first-order kinetics with kinetic constant of 2.0 x 10(-3) to 5.5 x 10(-3) Lg(-1) min(-1) was proposed along with a possible mechanism. 4-nitrocatechol, 4-nitropyrogallol, 1,2,4-trihydroxybenzene, hydroquinone, acrylic acid, malonic acid, and oxalic acid were identified in the oxidation products. CONCLUSION: Introduction of Fe(III)-, Co(II)- and Ni(II)- into MCM-41 by impregnation produced effective catalysts for wet oxidation of 4-nitrophenol. The catalysts were able to oxidize 4-NP even without the presence of an oxidizing agent. The results suggest that the transition metal loaded MCM41 brings about a more effective interaction between 4-NP molecules and OH radicals. (c) 2008 Society of Chemical Industry.