Low-Concentration Methane Detection in Air Using Pt- and Pd-Modified SnO ₂ Nanocrystals: Role of Lattice Oxygen and Distinct Sensitization Mechanisms

Methane (CH 4 ) is a flammable greenhouse gas that must be detected reliably for industrial safety and environmental monitoring. Although SnO 2 -based chemiresistive sensors have been widely studied, CH 4 detection remains challenging because of the high C−H bond dissociation energy and the weak interaction of CH 4 with oxide surfaces. Here, Pt- and Pd-modified SnO 2 nanocrystals were systematically compared by correlating gas-sensing performance with CO pulse chemisorption, temperature-programmed desorption (TPD), CH 4 temperature-programmed surface reaction (CH 4 -TPSR), operando diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS), and in situ Raman spectroscopy. Among the samples examined, 5 wt % Pt-SnO 2 exhibited the highest response to 500 ppm CH 4, reaching 63 at 350 °C, whereas 5 wt % Pd-SnO 2 showed a lower maximum response of 34 at 300 °C. Both sensors responded reproducibly over the 10–500 ppm range, demonstrating low-concentration methane detection in air. CH 4 -TPSR and NH 3 -TPD showed that Pd-SnO 2 promotes methane activation more effectively at lower temperatures, consistent with its higher catalytic activity. In contrast, operando DRIFTS, O 2 -dependent sensing, and in situ Raman measurements revealed that Pt-SnO 2 undergoes stronger surface reduction and greater lattice-oxygen involvement during CH 4 oxidation, leading to stronger depletion-layer perturbation and a larger chemiresistive response. These results indicate that Pd predominantly enhances chemical sensitization, whereas Pt provides a more favorable coupling between methane oxidation and electronic modulation of the SnO 2 support. This study demonstrates a highly sensitive chemiresistive sensor for low-concentration methane detection in air and clarifies the distinct mechanistic roles of Pt and Pd in SnO 2 -based methane sensing.