Study of carbon-supported copper catalysts from orange peels − Preparation, characterization, and application in α-pinene oxidation

The use of orange peel as a precursor for activated carbon (AC) is a promising way to valorize this waste due to its ease of acquisition and the high elemental carbon content of this raw material. In this study, two different methods for the synthesis of carbon catalysts based on AC from biomass were presented. In these methods, H₃PO₄ was used as the chemical activator, while Cu (NO₃)₂ acted as the metal precursor for the active phase of the catalyst. Copper was introduced into the carbon material at different stages of preparation (before and after carbonization). The catalysts were characterized using FTIR, XRD, SEM, EDX and XPS. The textural properties were investigated using N₂ sorption at -196 °C. These materials were successfully used in the oxidation of α-pinene and the conversion of this cheap terpene into compounds of great industrial importance (α-pinene oxide, verbenone and verbenol). The results showed that the material prepared by impregnating the already prepared carbon support (AC_5%Cu_impregnation) was more active. For this catalyst, the conversion of α-pinene was 53 mol%, while this value for AC_5%Cu_oven sample was 43 mol%. The selectivity of the α-pinene oxide was 48 mol% for AC_5%Cu_impregnation sample and 39 mol% for AC_5%Cu_oven catalyst. The selectivities of the other products eg. verbenone and verbenol were not significantly different for both catalysts. Considering catalytic activity, it was found that a better method of prepared catalysts for use in the α-pinene oxidation was impregnation of carbonaceous support with a copper salt solution after the carbonization process.