SnO2 nanoparticles loaded with 0.2-2 wt% Pt have successfully been synthesized in a single step by flame spray pyrolysis (FSP) and investigated for gas sensing towards hydrogen (H-2). According to characterization results by X-ray diffraction, nitrogen adsorption, scanning/high resolution-transmission electron microscopy and analyses based on Hume-Rothery rules using atomic radii, crystal structure, electronegativities, and valency/oxidation states of Pt and Sn, it is conclusive that Pt is not solute in SnO2 crystal but forms nanoparticles loaded on SnO2 surface. H-2 gas sensing was studied at 200-10,000 ppm and 150-350 degrees C in dry air. It was found that H-2 response was enhanced by more than one order of magnitude with a small Pt loading concentration of 0.2 wt% but further increase of Pt loading amount resulted in deteriorated H-2-sensing performance. The optimal SnO2 sensing film (0.2 wt% Pt-loaded SnO2, 20 mu m in thickness) showed an optimum H-2 response of similar to 150.2 at 10,000 ppm and very short response time in a few seconds at a low optimal operating temperature of 200 degrees C. In addition, the response tended to increase linearly and the response times decreased drastically with increasing H-2 concentration. Moreover, the selectivity against carbon monoxide (CO) and acetylene (C2H2) gases was also found to be considerably improved with the small amount of Pt loading. The H-2 response dependence on Pt concentration can be explained based on the spillover mechanism, which is highly effective only when Pt catalyst is well-dispersed at the low Pt loading concentration of 0.2 wt%. (C) 2014 Elsevier B.V. All rights reserved.