| Summary: | To obtain a nanocrystalline SnO<sub>2</sub> matrix and mono- and bimetallic nanocomposites SnO<sub>2</sub>/Pd, SnO<sub>2</sub>/Pt, and SnO<sub>2</sub>/PtPd, a flame spray pyrolysis with subsequent impregnation was used. The materials were characterized using X-ray diffraction (XRD), a single-point BET method, transmission electron microscopy (TEM), and high angle annular dark field scanning transmission electron microscopy (HAADF-STEM) with energy dispersive X-ray (EDX) mapping. The electronic state of the metals in mono- and bimetallic clusters was determined using X-ray photoelectron spectroscopy (XPS). The active surface sites were investigated using the Fourier Transform infrared spectroscopy (FTIR) and thermo-programmed reduction with hydrogen (TPR-H<sub>2</sub>) methods. The sensor response of blank SnO<sub>2</sub> and nanocomposites had a carbon monoxide (CO) level of 6.7 ppm and was determined in the temperature range 60⁻300 °C in dry (Relative Humidity (RH) = 0%) and humid (RH = 20%) air. The sensor properties of the mono- and bimetallic nanocomposites were analyzed on the basis of information on the electronic state, the distribution of modifiers in SnO<sub>2</sub> matrix, and active surface centers. For SnO<sub>2</sub>/PtPd, the combined effect of the modifiers on the electrophysical properties of SnO<sub>2</sub> explained the inversion of sensor response from <i>n</i>- to <i>p</i>-types observed in dry conditions.
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