Efficient non-noble Ni–Cu based catalysts for the valorization of palmitic acid through a decarboxylation reaction

Abstract

The production of n-paraffins from biomass derivatives appears as an alternative to petroleum-derived compounds for the production of fuels, energy, and chemicals. Deoxygenation reactions, especially decarboxylation (DCX), are economically viable and are generally carried out with noble metal catalysts (Pt and Pd). Taking into account the cost and deactivation issues related to these catalysts, the development of non-noble metal catalysts is highly desirable yet challenging. For this purpose, non-noble monometallic catalysts (Ni, Fe, Cu, and Ag) and Ni-based bimetallic catalysts were studied for the DCX of palmitic acid (PA). Surprisingly, Ni–Cu/C systems were by far the most advantageous; the presence of Cu prevents the deactivation of the catalyst, decreases the reduction temperature, and significantly improves the yield of n-pentadecane (n-PD). The as-prepared catalysts formed a Ni–Cu alloy, but Cu- and Ni-rich phases were formed upon annealing. The higher Ni content in the 10% Ni 10% Cu/C catalyst resulted in a higher proportion of metallic Ni on the surface and a higher charge transfer from Ni to Cu. Thus, the best catalytic performance with full PA conversion and 95% selectivity to n-PD in 6 h was obtained at 320 °C, using 10 vol% of H₂ in N₂ and an operating pressure of 40 bar. Furthermore, this catalyst exhibited excellent recyclability under similar reaction conditions. Mechanistic studies confirmed the high catalyst selectivity, and excellent performance was observed for the DCX of stearic acid. This highlights the potential of this Ni–Cu catalyst for DCX of other fatty acids.