Structural origins of selectivity in guaiacol hydrodeoxygenation on copper

Abstract

Efficient upgrading of lignin-derived bio-oils requires selective hydrodeoxygenation (HDO) of oxygen-containing groups without hydrogenating the aromatic ring, a central challenge in biomass valorization. Here we combine density functional theory and microkinetic simulations to elucidate the HDO mechanism of guaiacol on copper catalysts. Across Cu(100), Cu(111), and Cu(211) surfaces, two competing routes dominate product distribution: (1) hydrogen-assisted deoxygenation (H-DO) via methoxy dissociation, producing phenol, and (2) partial hydrogenation (PHDO) of the aromatic ring, leading to cyclohexanone-type products. We show that H-DO activity is largely insensitive to surface orientation due to weak Cu-C₂ interactions, whereas PHDO activity depends strongly on surface structure through Cu-C₃/C₆ bonding. This difference establishes the d-band center as a reliable electronic descriptor for selectivity. Cu(111), with its more negative d-band center and weaker adsorption, exhibits the highest aromatic selectivity. Guided by this insight, we propose and validate grain boundary (GB) engineering as a design strategy: Cu(111)/(111) GB selectively suppresses PHDO by destabilizing hydrogenation transition states, while retaining H-DO activity. These results establish a clear structure-activity-selectivity relationship for guaiacol HDO and demonstrate that electronic tuning through facet and GB control provides a general framework for designing metal catalysts for selective biomass upgrading.