A 0.65% Pt/SiO2 catalyst has been prepared using an ion exchange technique and extensively characterized prior to being used for continuous catalytic N2O reduction by H2 at very low temperatures, such as 363 K. The supported Pt with a high dispersion of 92% gave no presence of O atoms remaining on an H-covered Pts, based on in situ DRIFTS spectra of CO adsorbed on Pts after either N2O decomposition at 363 K or subsequent exposure to H2 for more than 1 h; thus the residual uptake gravimetrically observed even after the hydrogen titration on an O-covered surface is associated with H2O produced by introducing H2 at 363 K onto the oxidized Pts. Dissociative N2O adsorption at 363 K on Pts was not inhibited by the H2O(ad) on the silica surface but not on Pts, as acquired by IR peaks at 3,437 and 1,641 cm.1, in very consistent with the same hydrogen coverage, established via H2-N2O titration on a reduced Pts, as that revealed upon the titration reaction with a fully wet surface on which all bands and their position in IR spectra for CO are very similar to that obtained after H2 titration on a reduced Pts. Based on the characterization using chemisorption and in situ DRIFTS and TPD measurements, the complete loss in the rate of N2O decomposition at 363 K after a certain on-stream hour, depending significantly on N2O concentrations used, is due to self-poisoning by the strong chemisorption of O atoms on Pts, while the presence of H2 as a reductant could readily catalyze continuous N2O reduction at 363 K that is a greatly lower temperature than that reported earlier in the literature.