Efficient catalytic hydrodeoxygenation of palmitic acid over N-doped carbon-supported Ni catalysts: A Combined Experimental, kinetic and DFT study

The catalytic hydrodeoxygenation (HDO) of biomass-derived bio-oil to produce hydrocarbon-rich liquid fuels is a key step for the high-value energy utilization of biomass. In this work, a novel nitrogen-rich polymer, poly-o-phenylenediamine (PoPD), was first synthesized and used as a nitrogen source to prepare a series of lignin-derived carbon-supported Ni-based catalysts (Ni/NxC, where x  = 0, 1, 3, 5, 7, and 9 wt%) with varying nitrogen doping levels. Among them, Ni/N3C catalyst exhibited the smallest Ni nanoparticle size, the highest dispersion of active metals, and the strongest metal-support interaction as compared to other catalysts. Moreover, under the optimal parameters, the Ni/N3C catalyst provided the highest conversion of palmitic acid (100%) and the highest overall yield of HDO products (86.06%). The quite outstanding performance of Ni/N3C is attributed to the synergistic effect between its rich surface oxygen vacancies, which efficiently adsorb the oxygen-containing functional groups of palmitic acid, and the superior hydrogen dissociation capability of the Ni nanoparticles. Reaction kinetic modeling results revealed that at elevated temperatures, the pathway for the dealkylation of pentadecane to form shorter-chain alkanes serves as the rate-determining step for the entire system. DFT calculations revealed that the DCO_x and HDO pathways are the primary reaction routes occurring in the whole system. According to the aforementioned research, the mechanism of the Ni/N3C-catalyzed HDO of palmitic acid has been proposed in detail. This work provides an innovative strategy for the effective conversion of oxygen-rich biocrude into hydrocarbon-enriched liquid fuels.