Study of the interaction of nitric oxide with Cu(100) and Cu(111) surfaces using low energy electron diffraction and electron spectroscopy

Abstract

The adsorption of nitric oxide on Cu(lO0) and Cu(l11) surfaces has been studied by combining X-ray and U.V. photoelectron spectroscopy with low energy electron diffraction. At 80K two molecular states, characterised by N(1s) values of 399.5 and 401 eV, have been assigned to '' bent " and " linear " configurations, respectively, The bent form dissociates slowly at 80 K while the h e a r species desorbs above z 170 K. Assignments of the " bent " and " linear " forms were facilitated by recourse to the known sterochemistry of metal nitrosyl complexes where a correlation between formal charge on the ligand and sterochemistry has been established. Furthermore the results are compared with the adsorption of NO on both clean nickel and nickel whose surface reactivity has been controlled by pre-exposure to oxygen.The N-adatoms arising from dissociation at 80 K are mobile and highly reactive forming N20 which remains on the surface at this temperature. There is no evidence for dinitrogen desorption.The N 2 0 was characterised by both its X-ray and U.V. photoelectron spectra. Cu(100) and Cu(ll1) behave similarly, Cu(ll1) being less active than Cu(100) in dissociation. At 80 K with Cu(100) there is evidence from LEED for the formation of an ordered (2/2xd/2)R45" structure superimposed on an increase in the background intensity of the scattered electrons. On warming the adlayer to 290 K well ordered (2/Zx1/2)R45"-0 structures are present. No ordered structures were observed with Cu(l11) at either 80 or 290 K and this is compatible with previous studies of chemisorbed oxygen on Cu(ll1). At 290 K NO chemisorbed dissociatively on Cu(100) and Cu(l11) both fragments being retained at the surface. With Cu(100) the symmetry of the adlayer conformed to a ( 2 / 2 x 4 5 ~4 5 0 structure. From a curve fitting analysis of the O(1s) data for the adlayer formed on Cu(100) concentrations of the individual surface species O(a), NO(a) and N20(a) present at 80 K and on thermal activation to 110, 133 and 290 K were calculated.A detailed understanding of the mechanism of inherently simple surface processes is essential for the development of models for more complex heterogeneously catalysed reactions. This is clear from the impact that the early studies of Langmuir (see Suits)l and J. K. Roberts had on the future development of the subject. X-ray photoelectron spectroscopy (X.P.S.) offers a new dimension to the study of molecular processes occurring at solid surfaces in that it allows the chemical identification of all elements (other than hydrogen) ; furthermore, the measured core-electron binding energies are sensitive to the chemical environment of the atom in question. Ultraviolet photoelectron spectroscopy (u.P.s.) provides an important adjunct to X.P.S. in that it gives more direct information on the electron density of states close to the Fermi level of the substrate and also reflects changes in the latter after gas adsorption. By making direct comparison with the photoelectron spectrum of the gaseous molecule (the " finger print " appro...

Elements Science and Technology Project: Design of Precious Metal Free Catalyst for NO Dissociation

“…For both cases, the dissociation proceeds in which the O atom is detached from the N atom and moves to the next fcc hollow site. It was experimentally identified that adsorbed NO on bent structure is the precursor for dissociation and agrees with the dissociation geometry obtained in our work 27) . In all stages, the distance between the N and O atoms is larger if it is on Cu _ Cu2O(111) than on Cu(111).…”

“…By combining X-ray and UV photoelectron spectroscopy with low energy electron diffraction (LEED), Johnson et al found that adsorbed NO on Cu(111) in a bent configuration dissociated slowly at 80 K while the linearly adsorbed molecule desorbed upon heating the crystal at 170 K 27) . Nonetheless, it was not concluded whether the bent or linear structure was the initial adsorption structure but it was specified that the bent structure as precursor for NO dissociation.…”

Energetics and Dynamics for NO and CO Dissociation on Cu(100) and Cu(111)

“…In addition, the dissociation of CO and NO proceeds much easier on the more open Cu(100) surface than on the close-packed Cu(111) surface, in agreement with experiments that show a greater reactivity for more open surfaces toward NO dissociation. 16,17,50 Another interesting conclusion can be made by comparing the bridged and diagonal reaction paths on either surface. On Cu(111), it is clearly the diagonal reaction path that is energetically favored for all systems studied, since we could rule out the bridged pathway that is too short for bringing about the dissociation.…”

Formation of unique trimer of nitric oxide on Cu(111)

“…On Cu(111), the initial adsorption state of NO at T ≈ 100 K was reported to be a monomeric species. [26][27][28][29][30][31][32] The bonding geometry was initially proposed to be a bent structure on the bridge site, based on comparison with the N-O stretching frequency of nitrosyl complexes. [26][27][28] However, the use of the vibrational frequency as a guide to determining the bonding site of NO on a metal surface was questioned, 33 and an upright NO molecule on the threefold site was proposed as a candidate for the adsorption structure on Cu(111).…”