Hydrodeoxygenation of m-cresol over bimetallic NiFe alloys: Kinetics and thermodynamics insight into reaction mechanism

Abstract

Developing mechanistic insights into the reaction network of hydrodeoxygenation (HDO) of lignin-derived compounds is key to rational design of high-performance catalysts for bio-oils upgrading. Herein, we present a comprehensive theoretical study on HDO of m-cresol, a model compound of phenolics, on Ni(1 1 1) and NiFe(1 1 1) surfaces using periodic density functional theory calculations and microkinetic modeling techniques, with a focus on the several competing reaction pathways including enol-keto tautomerization, hydrogenation, and dehydroxylation. Our results show that the activation of the COH bond of m-cresol and phenolic intermediates can be greatly promoted on oxophilic NiFe(1 1 1), evidenced by the elongated COH bond length and the enhanced dehydroxylation activity with respect to Ni(1 1 1). It is found that m-cresol HDO on NiFe(1 1 1) shares certain common features with that on Ni(1 1 1), but exhibits important differences that result in dramatic changes in selectivity. We show that the COH bond length of adsorbed phenolic intermediates can be used as a good descriptor for prediction on the COH bond scission reaction in HDO. Finally, microkinetic modeling augmented by degree of rate control analysis is applied to rationalize the experimentally-observed differences in product distributions over Ni and NiFe catalysts when kinetic factors still dominate.