Microscopic studies of NO2 on Ag(1 1 0)–p(2×1)-O and reactivity of surface nitrate

It has been shown previously with temperature programmed reaction spectroscopy (TPRS) and high resolution electron energy loss spectroscopy that NO2 adsorption on Ag(1 1 0)–p(2×1)-O at room temperature leads to the formation of surface nitrate, NO3(a), which, when heated, decomposes into NO(g) and N(a) at 475 K; the latter recombines with O(a) to form NO(g) at 530 K. We have reexamined this reaction using scanning tunneling microscopy in combination with TPRS and low energy electron diffraction (LEED). The present study shows that NO3(a) formed at room temperature yields straight rows at low coverage and jagged rows at high coverage along the [0 0 1] direction, which exhibit p(4×1) and c(6×2) LEED patterns, respectively. Nitrate formation results in the formation of pits one layer deep on about 18% of the terrace area and severely roughens step edges, indicative of the incorporation of silver atoms into the nitrate structure. This surface nitrate species is found to be reactive toward CO oxidation. Annealing the nitrate adlayer to 485 K results in the formation of zigzag rows comprised of N(a) and O(a) atoms. Oxygen in this structure is not reactive with CO. Surface structure models are suggested for adsorbed nitrate and coadsorbed N and O.