Interplay between Surface Reconstruction and Redox State Controls CO2 Activation on α-Fe2O3(012) Single-Crystal Surfaces

Abstract

Although Fe reduction is frequently linked to CO2 activation on iron oxides, it remains unclear whether reactivity originates from the oxidation state itself or from the local environment in which reduced Fe species are formed. Here, near-ambient-pressure X-ray photoelectron spectroscopy combined with low-energy electron diffraction is used to address this question by comparing CO2 activation on two well-defined α-Fe2O3(012) surface terminations with distinct local Fe environments. On the (1 × 1) termination, H2 exposure induces partial surface reduction and generates Fe2+ species that enable subsequent CO2 activation, leading to the formation of activated CO2– intermediates identified by a C 1s feature at 288.7 eV. In contrast, the reconstructed (2 × 1) termination exhibits a distinct response toward CO2 despite the presence of Fe2+ species; instead, CO2 exposure favors bicarbonate-related species formation and reoxidizes surface Fe2+ to Fe3+. This termination-dependent response demonstrates that CO2 activation on α-Fe2O3(012) is governed not only by Fe oxidation state but also by the local environment in which reduced Fe species are stabilized. These findings establish that reduced Fe sites become reactive only in specific surface environments, providing mechanistic insight into the structure–reactivity relationships governing CO2 activation on iron oxide catalysts.