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.