A combined transient and computational study of the dissociation of N2O on platinum catalysts

The energetics of the low-temperature adsorption and decomposition of nitrous oxide, N2O, on flat and stepped platinum surfaces were calculated using density-functional theory (DFT). The results show that the preferred adsorption site for N2O is an atop site, bound upright via the terminal nitrogen. The molecule is only weakly chemisorbed to the platinum surface. The decomposition barriers on flat (111) surfaces and stepped (211) surfaces are similar. While the barrier for N2O dissociation is relatively small, the surface rapidly becomes poisoned by adsorbed oxygen. These findings are supported by experimental results of pulsed N2O decomposition with 5% Pt/SiO2 and bismuth-modified Pt/C catalysts. At low temperature, decomposition occurs but self-poisoning by O(ads) prevents further decomposition. At higher temperatures some desorption of O2 is observed, allowing continued catalytic activity. The study with bismuth-modified Pt/C catalysts showed that, although the activation barriers calculated for both terraces and steps were similar, the actual rate was different for the two surfaces. Steps were found experimentally to be more active than terraces and this is attributed to differences in the preexponential term.