Reduction of N2O by NH3 on polycrystalline copper and Cu(1 1 0): A combined XPS, FT-IRRAS and kinetics investigation

Kinetics of N2O decomposition and catalytic reduction of N2O by NH3 in the presence or absence of oxygen have been studied on polycrystalline Cu planar chip (3 cm × 3 cm × 0.1 cm) or Cu(1 1 0) single crystal, using catalytic test equipment, XPS and FT-IRRAS techniques. It has been shown that N2O decomposes on metallic Cu, but gives then Cu2O, which is detrimental to N2O decomposition. The presence of a reductant, such as NH3, allowed N2O to react leading to its catalytic reduction to N2; 500 °C is the best temperature for catalytic reduction alone, i.e. with low additional self-decomposition of N2O or NH3. The presence of oxygen, in amount less than that of NH3, leads to more efficient NH3 oxidation, oxygen being observed to be more reactive than N2O on NH3. XPS results enabled to identify the active surface as metallic Cu and Cu3N for NH3 oxidation and NH2, NH, N adsorbed species as intermediates of the reaction. At room temperature, in the presence of N2O, O2 and NH3, FT-IRRAS allowed to show the formation of NH2 and NH species (bands at 1550 and 1440 cm−1, respectively) and of two N2δ− species (bands at 2170 and 2204 cm−1), the latter one corresponding to adsorbed N2δ− species close to adsorbed electron accepting O or OH species. This study demonstrated that N2O decomposed to N2 and O species during SCR reaction; it enabled to identify several adsorbed surface species (N, NH, NH2, N2δ−), both by XPS after catalytic reaction at 500 °C on the polycrystalline Cu chip and by IRRAS on Cu(1 1 0) single crystal in the presence of the reactants at room temperature. In addition, it was shown that N2 is a powerful IR probe to characterise the surrounding environment of surface sites that cannot be identified by any other way.