Oxidative property of Nb-containing MCM-41 molecular sieves for vapor phase oxidation of m-toluidine

Abstract

Mesoporous Nb-MCM-41 molecular sieves (Si/Nb = 50 and 75) were synthesized hydrothermally. As-synthesized and calcined catalysts were characterized by low angle X-ray powder diffraction (XRD), N2-adsorption isotherm, thermogravimetric and FT-IR techniques. The niobium impregnated MCM-41 catalysts were also prepared by wet method and their structure was elucidated XRD and FT-IR spectroscopy. Electron spinning resonance (ESR) studies conformed the co-ordination environment of niobium in both type of catalysts. The catalytic activity of the above catalysts was studied for the vapor phase oxidation of m-toluidine with CO2-free air at 200, 250, 300, 350, 400 °C. The major products were m-aminobenzoic acid and m-aminobenzaldehyde. The m-toluidine conversion was found to be higher in niobium impregnated catalysts than incorporated catalysts. The selectivity to m-aminobenzoic acid, which was the principally aimed product in this study, was found to be higher than that of the m-aminobenzaldehyde. The activities of catalysts follow the order Nb-MCM-41 (1%) > Nb-MCM-41 (2%) > Nb-MCM-41 (3%) > Nb-MCM-41 (50) > Nb-MCM-41 (75). The effect of weight hourly space velocity and time on stream was also studied on conversion and products selectivity and the results are discussed. Conditions were optimized for better m-toluidine conversion and products selectivity.