Theoretical Study Of Methane Conversion Catalyzed By Transition Metal Doped Vanadium Oxide Clusters

As the main ingredient in natural gas,methane(CH₄)has become one of the most promising energy resources due to its high H/C ratio and affluence of the reserves in worldwide scale.Efficient catalysts for direct conversion of CH₄ to produce value-added liquid oxygenates under ambient condition has long been pursued but remains challenging.The intrinsic high stability of CH₄ molecule makes the oxidation reaction difficult to be started and controlled.Transition metal compounds play an exclusive role in CH₄ oxidation,but deep understanding of the reaction mechanism and fundamental rule for tailoring the activity of catalysts is lacking and highly desirable.Using ab initio calculations,herein we show that magnetic[V₂O₅]_n(n=2,3,4)clusters doped by group IVB elements(Ti/Zr/Hf)possess unique activity and selectivity for CH₄oxidation with CO/O₂ gas mixture.Systematical assessment of various common functionals has found that Tao–Perdew–Staroverov–Scuseria functional(TPSS for short)accompanied with SDD basis set for V/Ti/Zr/Hf/Sc/Y and 6-311+G(d,p)for C/H/O is the best methodology for describing the adsorption configuration.Liquid chemicals are produced with low barriers of only 0.99 e V for CH₃COOH and 1.01 e V for CH₃OH,respectively.The oxidation reaction follows Mars-van Krevelen mechanism in the presence of our doped vanadium oxide clusters and the donation of an oxygen atom from the cluster to the methyl productions may expose doped transition metals.Thus,effective adsorption of CH₄ on catalysts and replenishment of the active oxygens are the key to catalytic CH₄ oxidation reaction.Intriguingly,the adsorptions of CH₄ and O₂ on the clusters are found mutually restrained with each other,which mediates the catalytic activity.Finally,the activity originates from the O atoms bonded with dopants and having spin multiplet,which govern the single electron transfer from CH₄ and enable C-H homolytic cleavage.Thus,as the adsorption energy of H-CH₃ molecule is weakened,the acceptability for unpaired electrons of catalysts decreases,which can be linearly correlated with the p band center difference between majority and minority spin channels of the active O atoms.This electronic structure-activity relationship provides new insights for atomically precise design of nanometer and subnanometer catalysts for highly efficient CH₄ conversion.