Oxidation of limonene over molybdenum dioxide-containing nanoporous carbon catalysts as a simple effective method for the utilization of waste orange peels

Abstract

A new method of the oxidation of natural limonene, obtained from waste orange peels, using relatively inexpensive MoO2-containing activated carbon catalysts is presented. The contents of molybdenum in the catalysts were equal to 0.68, 1.32, and 2.64 wt%, and these new materials were investigated using various instrumental methods (ICP-AES, XRD, SEM, and GC), as well as liquid nitrogen sorption. The oxidation of limonene was performed separately with H2O2 and t-butyl hydroperoxide (TBHP) as the oxidants under the following conditions: temperature of 70 °C, molar ratio of limonene/oxidant = 1:2, methanol concentration 95 wt%, catalyst content 2.45 wt%, and reaction times of 0.5–72 h. All catalysts were active in the oxidation of limonene. With H2O2 as the oxidant, carveol (selectivity of 42–65 mol%) and perillyl alcohol (selectivity of 10–30 mol%) were the main products of the limonene oxidation, and carvone and 1,2-epoxylimonene diol were by-products. For the oxidations with TBHP, the conversion of limonene was lower than with hydrogen peroxide. This new environmentally friendly method allows for the transformation of organic waste material into industrially important value-added products.