A cleaner route for hydrodeoxygenation of oleic acid in hexane containing pressurized CO2 over a MCF supported Fe-Pd-Ni trimetallic catalyst

Abstract

Selective production of octadecane through the hydrodeoxygenation of oleic acid in hexane containing pressurized CO2, a green reaction media, using a mesocellular foam (MCF) supported Fe-Pd-Ni/MCF catalyst was demonstrated in this study. In addition to hexane containing pressurized CO2 playing a key role in directing the hydrotreatment of oleic acid towards hydrodeoxygenation over decarboxylation/decarbonylation, the use of MCF as the support helped achieve higher selectivity for octadecane, the major hydrodeoxygenation product while at the same time completely negating heptadecane, the decarboxylation/decarbonylation product. Negligible diffusion resistance aided by the 3-dimensional cage like structure and large pore opening of MCF, plus a better dispersion of the catalyst were identified as major reasons for enhancement of octadecane yield. An octadecane yield of 93% at 4 h was achieved through an optimization of temperature to 278 °C and a H2 pressure to 40 bars, while the CO2 pressure was kept constant at 20 bars. The activation energy for the hydrodeoxygenation of stearic acid to octadecane was observed to be a 43.6% reduction over the existing literature. An increased spillover of H2 onto the surface of Fe nanoparticles, triggered by an increased sticking capability of H2 on Pd-Ni alloy patches formed on the top Fe nanoparticles, was proposed as the major reason for this acceleration. The proposed catalyst could not only avoid production of undesired decarbonized product heptadecane but also reduce energy requirement to achieve higher yield over reported data due to the lowering of temperature and time, indicating its superiority.