Understanding the role of Ni-based single-atom alloys on the selective hydrodeoxygenation of bio-oils

Abstract

In the search for sustainable fuels, high-performing, cost-effective, and abundant catalysts are needed for bio-oils hydrodeoxygenation refining, with single-atom-alloy (SAA) catalysts showing potential for outstanding activity and economic bi-metallic assembly. Hydrodeoxygenation upgrading of modelled bio-oil molecules, namely, phenol, anisole, benzaldehyde, and vanillin, has been systematically explored here over a wide-range of SAA Ni(111)-based catalysts (Pd, Pt, Cu, Co, Fe, Ru, Re, Rh, V, W, and Mo) using density functional theory (DFT) and microkinetic modeling. Stability, adsorptive, and activity structural-property-relationships were established for bio-oil derivatives that can direct the synthesis process of cost-effective SAA combinations. DFT revealed the thermodynamic atomic dispersion tendency of the SAA catalysts. Furthermore, the OH*- and O*$-$induced on the catalyst surface enhanced the SAA upper-layer stability. Single-atoms shifted the d-band center towards the fermi-level in agreement with bio-oils adsorption energies and C_aryl$-$O lengths. The free-energy pathways at 573 K unveiled the SAAs role in lowering the activation barriers, with WNi(111) best-performing towards selective phenol and anisole direct deoxygenation, whilst MoNi(111) directs the facile activation of benzaldehyde and vanillin CO scission. The microkinetic/thermodynamic analysis of O*-poisoning showed that MoNi(111) withstands high O*-coverage, indicative by higher deoxygeneration rates in 350-950 K and greater coverage of the desired product.