Hydrodeoxygenation Of M-Cresol Over Bimetallic NiFe Alloys:Kinetics And Thermodynamics Insight Into Reaction Mechanism

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 mcresol,a model compound of phenolics,on Ni(111)and NiFe(111)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 C-OH bond of m-cresol and phenolic intermediates can be greatly promoted on oxophilic NiFe(111),evidenced by the elongated C-OH bond length and the enhanced dehydroxylation activity with respect to Ni(111).Technically,the C-OH bond length of adsorbed phenolic intermediates can be used as a good descriptor for prediction on the C-OH bond scission reaction in HDO.It is found that m-cresol HDO on NiFe(111)shares certain common features with that on Ni(111),but exhibits important differences that result in dramatic changes in selectivity.The degree of rate control analysis suggests that the rate-determining steps for MCONE,MCOL and TOLproduction on Ni(111)are most likely to be the tautomarization of 13 to 12,the ring hydrogenation of 13,and the C-OH cleavage via the partial hydrogenation,respectively,while for TOL production on NiFe(111)is most likely to be the C-O direct cleavage.Our detailed microkinetic modeling analysis explains the experimentally-observed differences in product distributions over Ni and NiFe catalysts when kinetic factors still dominate.