Pt-Triggered Reversal in Acetone Sensing: Crystal Phase-Dependent Dispersion Governs Performance of Fe2O3

The crystal phase of metal oxide supports critically governs the gas-sensing performance by modulating metal–support interactions. This study reveals a counterintuitive “reversal effect” induced by Pt modification on the acetone-sensing properties of γ-Fe2O3 and α-Fe2O3. Despite pristine α-Fe2O3 exhibiting a 9.4-fold higher response to acetone than γ-Fe2O3 (179 vs 19), even though the latter possesses a 4-fold larger specific surface area, Pt functionalization dramatically reverses this performance hierarchy. After loading 0.3 wt % Pt, Pt–Fe2O3-γ achieves an exceptional response of 1470 to 100 ppm acetone (77-fold enhancement over pristine γ-Fe2O3), whereas Pt–Fe2O3-α suffers a 9.4-fold reduction. Oxygen temperature-programmed desorption (O2-TPD) and structural characterization demonstrate that this reversal stems from the crystal phase-dependent Pt dispersion: γ-Fe2O3 facilitates atomic dispersion of Pt, optimizing gas adsorption and electron transfer, while α-Fe2O3 promotes Pt nanoparticle aggregation, which impedes charge transport despite enhanced oxygen adsorption. This work elucidates a new mechanism wherein the support crystal phase dictates noble metal dispersion states to control sensing behavior, providing a paradigm for designing phase-engineered sensing materials.