Catalytic reduction of N2O by H2 over well-characterized Pt surfaces

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 Pt _s , based on in situ DRIFTS spectra of CO adsorbed on Pt _s 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 Pt _s . Dissociative N₂O adsorption at 363 K on Pt _s was not inhibited by the H₂O_(ad) on the silica surface but not on Pt _s , 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 Pt _s , 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 Pt _s . 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 Pt _s , 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.