Aerial oxidation of p-isopropyltoluene over manganese containing mesoporous MCM-41 and Al-MCM-41 molecular sieves

Abstract

The catalytic activity of MCM-41 after impregnation with manganese species was investigated. Si-MCM-41 and Al-MCM-41 (Si/Al = 99 and 158) were synthesized by hydrothermal method. The XRD analysis shows that aluminium incorporated MCM-41 retains the hexagonal structure. The higher d-spacing values of Al-MCM-41 catalysts than that of pure MCM-41 indicate the incorporation of aluminium into the framework. Manganese oxide impregnated MCM-41 and Al-MCM-41 catalysts were also prepared by wet method. Their structures were confirmed by XRD. The presence of Mn 2+ was evident through DR UV–vis and ESR spectroscopy. The catalytic activity of the above catalysts was studied by vapour phase oxidation of p-isopropyltoluene ( p-cymene) with CO 2-free air in the temperature ranging from 200–400 °C. On comparison, the Mn-MCM-41 catalyst significantly shows higher p-cymene conversion and products selectivity. The major products were 4-methylacetophenone, 4-isopropylbenzaldehyde, 1,2-epoxyisopropylbenzaldehyde and 4-methylstyrene. Among the products, selectivity to 4-methylacetophenone was found to be higher than others. Activities of the catalysts follow the order Mn-MCM-41 > Mn-AlMCM-41 (99) > Mn-AlMCM-41 (158). Reaction conditions were optimized on better conversion and products selectivity and the results are discussed.