Stepped M@Pt(211) (M = Co, Fe, Mo) single-atom alloys promote the deoxygenation of lignin-derived phenolics: mechanism, kinetics, and descriptors

Abstract

Low-coordination active sites are always intriguing for their unique functionality of promoting specific catalytic reactions. Herein, we employed stepped M@Pt(211) (M = Co, Fe, Mo) single-atom alloys (SAAs) to model undercoordinated sites for their deoxygenation activity against lignin-derived phenolics. Using the combined approach of DFT calculations and microkinetic modeling, we reveal that M@Pt(211) was superior over the flattened M@Pt(111) in promoting phenolic hydrodeoxygenation owing to the beneficial geometric effects of the low-coordinated step/edge sites rendering multiple viable adsorption modes (i.e., vertical and parallel). With more favorable M–O (phenolic) interaction, the conversion of phenol to benzene proceeded kinetically much faster on M@Pt(211) than on pristine Pt(211). The temperature-dependent TOFs increased steadily with the increasing reaction temperature from 400 K to 725 K, beyond which a plateau was almost approached. Likewise, the removal of adsorbed *OH could be effectively achieved by raising the H₂ pressure up to 5 bar. The oxophillicity of the alloyed M mattered most to the deoxygenation efficiency of M@Pt(211) and the optimal oxophillicity could be screened from the minimal difference in the reaction Gibbs free energy between direct deoxygenation and H₂O formation. Our study provides molecular-level insights into tuning the reaction parameter space and step/edge sites for the catalytic upgrading of phenolics.