Liquid phase hydrogenation of dementholized peppermint oil on Pt/Al2O3 catalysts: Part II. A study to determine deactivation causes Original Research Article

In a previous work it was observed that Pt/Al2O3 catalysts, prepared by wet impregnation, are deactivated during liquid phase hydrogenation of dementholized peppermint oil fractions. The aim of this work is to determine the main causes for this deactivation. Fourier transform infrared (FTIR), with and without chemisorbed carbon monoxide, temperature programmed desorption (TPD), temperature programmed hydrogenation (TPH) and gas phase cyclohexane dehydrogenation were used to characterize fresh and used Pt/Al2O3 catalysts. It was found that metal platinum active phase is mainly deactivated by strong adsorption of surface carboxylate-like species and/or unsaturated carbon compounds. These strongly adsorbed species are generated from the interaction of catalyst surface with decarbonylation products from menthone and other carbonyl compounds present in the dementholized peppermint oil fraction. In addition, it was found that Pt/Al2O3 catalyst can be reactivated in hydrogen flow at temperatures between 400–450 °C. Treatments in nitrogen flow led only to a partial regeneration of the catalysts. This is because hydrogen converted surface carboxylates and unsaturated carbon compounds into methane facilitating their removal.