Hydrogenation of Citral over Activated Carbon Cloth Catalyst

Catalytic hydrogenation of an (alpha),(beta)-unsaturated aldehyde, citral, over different Ni and Pt fiber catalysts as well as a commercial Pt powder catalyst was performed in a batch reactor under pressurized conditions. Active carbon was used as a support material. The influence of the important variables, such as temperature and pressure, was investigated in the batch reactor. The metal loading in the catalyst was varied as well. The catalysts were characterized with scanning electron microscopy, atomic force microscopy, N2-physisorption, temperature-programmed hydrogen desorption, and inductively coupled plasma mass spectroscopy. Four consecutive experiments were carried out with each fiber catalyst in the batch reactor to elucidate eventual catalyst deactivation. The decrease in activity was fairly notable. The results of the kinetic experiments demonstrated the feasibility of utilizing woven active carbon cloths as supports in three-phase metal-catalyzed hydrogenation of citral. The Ni on active carbon cloth (ACC) yielded citronellal, menthol, and isopulegol. Pt/ACC catalyst favored hydrogenation of the C=O group, i.e., the formation of geraniol and nerol, whereas the commercial Pt/AC powder catalyst led to citronellal and various other products of its hydrogenation. Possible limitations for application of Pt/ACC catalyst are associated with deteriorating activity as a pronounced deactivation was observed for the fiber catalyst.