Doping Ti as structural and electronic promoter in LaFeO3 for enhanced chemical looping dry reforming of methane

Abstract

The process efficiency of methane-to-syngas conversion via chemical looping technology suffers from the trade-off between high activity for C-H bond cleavage and high syngas selectivity, which is highly dependent on the precise regulation of M−O pair chemical state. Herein, we found that minor Ti doping as structural and electronic promoter in LaFeO₃ (LaFe_0.85Ti_0.15O₃) perovskite can greatly promote the activation of methane, rendering enhanced syngas yield 2.3-fold higher than LaFeO₃ while maintaining 99 % CO selectivity for chemical looping dry reforming of methane (CLDRM). Experimental studies and DFT calculation analysis revealed that substitution of Fe³⁺ by Ti⁴⁺ with smaller radius could reduce the Fe-O bond length and increase the Fe-O-Ti bond angle, which induced the enhanced Fe_3d-O_2p bond hybridization, leading slightly elevated Fe valence state. Besides, the formation of Fe-O-Ti motif could enrich the electron density over O-atom due to the higher capability of Ti in donating electrons than Fe. Such electronic effect of Fe-O in Fe-O-Ti motif greatly reduced the activation energy barrier for heterolytic cleavage of C-H bond in CH₄ from 1.88 eV (LaFeO₃) to 1.32 eV (Fe-O-Ti in Ti doped LaFeO₃), which could be instructive for designing advanced redox catalysts via precisely tuning the chemical state of M−O pair.