N2O adsorption and reaction at Pd(110)

The adsorption and decomposition of N2O on Pd(110) has been studied using molecular beam uptake measurements and reflection–absorption infrared spectroscopy to characterise the reaction products. Nitrous oxide adsorption at 300 K leads to efficient dissociation with an initial sticking probability S0=0.65. The reaction saturates at an uptake of 0.5 ML of adsorbed O, the surface forming an ordered Pd(110)-c(2×4)O overlayer. At higher temperatures the reaction probability drops, consistent with a trapping-dissociation mechanism. Adsorption at temperatures below 100 K leads to efficient dissociation, but the dissociation probability drops rapidly with uptake and thereafter N2O is adsorbed intact. A secondary maximum in the N2 product yield is seen for an N2O uptake of 0.5 ML, with the surface simultaneously ordering to form a (1×2) low-energy electron diffraction pattern that becomes sharp as uptake saturates with a composition of 0.15 ML O and 0.85 ML of N2O. We suggest that this structure is associated with a row-pairing reconstruction of Pd(110), forming a corrugated Pd surface. The IR spectrum shows bands at 1290 and 2262 cm−1 due to N2O adsorbed with a component of its axis perpendicular to the surface. Heating this surface leads to desorption of molecular N2O at 100 K, followed by two further peaks at 117 and 140 K with partial dissociation. We discuss the origin of the off-normal emission of N2 during N2O decomposition and the role of N2O as an intermediate during the reaction of NO on Pd(110).