Hydrodeoxygenation of guaiacol over bimetallic Fe-alloyed (Ni, Pt) surfaces: reaction mechanism, transition-state scaling relations and descriptor for predicting C-O bond scission reactivity

We examine the initial hydrodeoxygenation (HDO) of guaiacol on bimetallic NiFe(111) and PtFe(111) using the density functional theory. Our results show that on NiFe(111), direct C aryl -O bond breaking and dehydrogenation are preferred over hydrogenation, while on PtFe(111), hydrogenation and dehydrogenation are preferred over C aryl -O bond breaking. Catechol is the major product of guaiacol HDO on both Fe-alloyed surfaces via dehydrogenation of methoxy (OCH 3 ) followed by O-CH 2 bond scission being promoted by oxophilic Fe alloying. In comparison, the removal of the oxo functional group of guaiacol ( i.e. , C aryl(α) -OH, C aryl(β) -OCH 3 and C aryl(β) O-CH 3 bond breaking) on both Fe-alloyed surfaces is more facile energetically than those on monometallic Ni(111) and Pt(111) owing to oxophilic Fe active surface sites. It is confirmed that the C-O bond length of adsorbed intermediates can serve as a good descriptor for predicting the C-O bond scission reactivity of the lignin-derived phenolic compounds on metal surfaces depending on C-O bond scission types. Small means big: DFT-calculated C-O bond length of adsorbed intermediates can serve as a good descriptor for predicting the C-O bond scission reactivity of phenolics over metal catalysts.