Catalytic reduction of N_2O by H_2 over well-characterized Pt surfaces

摘要

A 0.65% Pt/SiO_2 catalyst has been prepared using an ion exchange technique and extensively characterized prior to being used for continuous catalytic N_2O reduction by H_2 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 N_2O decomposition at 363 K or subsequent exposure to H_2 for more than 1 h; thus the residual uptake gravimetrically observed even after the hydrogen titration on an O-covered surface is associated with H_2O produced by introducing H_2 at 363 K onto the oxidized Pt_s. Dissociative N_2O adsorption at 363 K on Pt_s was not inhibited by the H_2O_((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 H_2-N_2O 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 H_2 titration on a reduced Pt_s. Based on the characterization using chemisbrption and in situ DRIFTS and TPD measurements, the complete loss in the rate of N_2O decomposition at 363 K after a certain on-stream hour, depending significantly on N_2O concentrations used, is due to self-poisoning by the strong chemisorp-tion of O atoms on Pt_s, while the presence of H_2 as a reductant could readily catalyze continuous N_2O reduction at 363 K that is a greatly lower temperature than that reported earlier in the literature.