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 S-o=0.65. The reaction saturates at an uptake of 0.5 hit of adsorbed O, the surface forming an ordered Pd(110)-c(2 x 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 N-2 product yield is seen for an N2O uptake of 0.5 ML, with the surface simultaneously ordering to form a (1 x 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 It, followed by two further peaks at 117 and 140 K with partial dissociation. We discuss the origin of the off-normal emission of N-2 during N2O decomposition and the role of N2O as an intermediate during the reaction of NO on Pd(110). (C) 2000 Elsevier Science B.V. All rights reserved.