(425d) Screening of Novel Ni-Based Catalysts for Hydrodeoxygenation of Modelled Bio-Oils Using DFT

Hydrodeoxygenation (HDO) is among the most promising paths for lignocellulosic biomass-based bio-oils upgrading towards desirable end-products and commercial fuels. Catalyst design in the HDO process plays a vital role in the reaction kinetics and pathways. Hence, in an attempt to refine the properties of mono-catalysts, single-atom alloy (SAA) catalysts have emerged as a pioneer class of heterogenous bimetallic catalysts with tuned properties and surface chemistry. Density functional theory (DFT) can be used to identify feasible metallic combinations in addition to allocating the energy barriers of the bio-oils HDO pathway. In this contribution, spin-polarized DFT calculations have been performed to explore a wide-range of nickel-based single-atoms alloys denoted as M-Ni(111) (i.e. M = Pd, Pt, Cu, Co, Fe, Ru, Re, Rh, V, W, and Mo) for the upgrading of four modeled bio-oils; phenol, anisole, benzaldehyde, and vanillin. Aside from the single-atom effect on the surface stability and electronic properties, the effect of different functional groups on the bio-oil adsorption strength were also tackled in this work.

Results reveal that the presence of hydroxyl-rich environment gave rise to the SAA catalysts stability. Moreover, the dopant single-atoms induced the surface activity as depicted by the d-band shift towards the fermi-level in the Partial Density of States (PDOS), following the same order of enhanced adsorption energy (E_Ads), and reduced O-M surface separation distances. Among the studied bimetallic catalysts, V-Ni(111) SAA resulted in the strongest adsorption of all modelled bio-oil compounds, reflecting the oxophilic strength of the vanadium guest-metal. Moreover, correlating the SAA active-sites periodic group number with the bio-oils adsorption energies revealed a linear relationship. Furthermore, the computed HDO pathways unveil the outstanding performance of the SAA, especially V-Ni(111), in reducing the energy barriers towards desirable end-products and value-added fuels for both fresh and spent catalyst (i.e. O^*-induced) scenarios.