Mechanistic and Thermodynamic Insights into the Deoxygenation of Palm Oils using Ni2P Catalyst: A Combined Experimental and Theoretical Study

Abstract Deoxygenation (DX) is a key enhancement process for biomass-derived biofuel production. To understand the DX mechanism of palm oils, we performed experimental and computational studies to investigate the DX reaction of palmitic acid on Ni2P catalyst. Experimental characterization and catalytic testing demonstrated that the DX on unsupported (001)-Ni2P catalyst prefers the decarbonylation (DCO) pathway over the hydrodeoxygenation (HDO) pathway with the ratios between 2.17 and 4.13 to 1. Mechanistic study using density functional theory calculation revealed that the DX of butyric acid also prefers DCO over HDO pathway. Both experimental and computational results suggested that the decarboxylation (DCO2) pathway is unlikely. The computation results indicated that the rate-limiting step of HDO pathway is in the butanol to butane conversion (activation energy Ea = 1.99 eV), whereas that of the DCO pathway is found during the butanal to propane conversion (Ea = 1.52 eV). However, additional thermodynamic analysis accounting for hydrotreating reaction condition (H2 = 50 bars at 653 K) suggested that the rate-determining step for the DCO pathway is actually the hydrogenation of butyric acid. In addition, the thermodynamics analysis also suggests that increasing reaction temperature may increase selectivity of HDO pathway. The mechanistic insights gained from this study will be beneficial for the enhancement of DX process for biofuel production.