Selective re‑exposure of the dominant α‑MnO2 (110) facet: unraveling the intrinsic mechanism for boosted toluene oxidation

Selective regulation of α-MnO 2 (110) facet via doping-masking-alkaline etching. • The (110) facet dominates toluene oxidation over 0.4CMO-AT. • Cu doping masks the (110) facet, impairing O 2 adsorption. • Re-exposure optimizes O 2 adsorption and elongates the O-O bond. • (110) facet and dual vacancies boost lattice oxygen mobility and benzoate ring-opening. Regarding the ambiguity of the advantageous crystal facet of α-MnO 2 in the catalytic oxidation of toluene, this study proposes a “doping–masking–alkali etching–re‑exposure” strategy. Through Cu doping, the (110) facet is selectively masked, followed by alkali etching to selectively re‑expose the (110) facet. The intrinsic activity and regulation mechanism of the (110) facet for low‑temperature catalytic oxidation of toluene were systematically investigated. The results show that the 0.4CMO‑AT catalyst (0.4 mmol Cu‑doped α-MnO 2 after alkali etching) with selectively re‑exposed (110) facets achieves 90% toluene conversion at 209 °C, significantly outperforming 0.4CMO (0.4 mmol Cu‑doped α-MnO 2 , 280 °C) without re‑exposed (110) facets and MO (undoped α-MnO 2 , 229 °C) with unregulated facets. Density functional theory (DFT) calculations and experiments collectively demonstrate that the (110) facet significantly promotes O 2 adsorption and activation, and that the synergistic effect of oxygen vacancies enhances lattice oxygen migration, thereby reducing the reaction energy barrier. In-situ DRIFTS identifies benzoic acid as the rate‑determining intermediate, while DFT calculations further reveal that the re‑exposed (110) facet thermodynamically favors its stabilization and ring‑opening. This work provides fresh insights into how α-MnO 2 facet engineering can be utilized for the catalytic breakdown of volatile organic compounds (VOCs). A “doping-masking-alkali etching” strategy was employed to selectively re-expose the (110) facet of α-MnO 2 . This facet, in synergy with copper/oxygen vacancies, markedly enhances O 2 adsorption and activation while reducing the reaction energy barrier, thereby constructing an efficient redox cycle and boosting catalyst activity. Download: Download high-res image (119KB) Download: Download full-size image