Surface Science 163 (1985) 503-515

North-Holland, Amsterdam 503

ELECTRONIC MODEL FOR ENERGIES, RELAXATIONS AND RECONSTRUCTION TRENDS AT METAL SURFACES D. TOMANEK and K.H. BENNEMANN

Institut ftir Theoretische Physik, Freie UniversitGt Berlin, Arnimallee 14, D - 1000 Berlin 33, Germany

Received 8 March 1985; accepted for publication 7 June 1985

A695

Surface energies and relaxations are calculated within the tight-binding formalism and includ-

ing also repulsive interatomic interactions. At fee and bee metal surfaces we obtain damped

oscillatory multilayer relaxations. Furthermore, we present results for the reconstruction at clean

(110) and (100) surfaces of Ir, Pt and Au. CO-suppressed and H-induced reconstruction observed

at some transition metal surfaces is quantitatively explained by coverage-dependent correction

terms to surface energies.

516 Surface Science 163 (1985) 516-540

North-Holland, Amsterdam

REACTION OF METHANOL WITH Cu(ll1) AND Cu(ll1) + O(ads)

J.N. RUSSELL, Jr., S.M. GATES and J.T. YATES, Jr.

SurJace Science Center, Department of Chemistry University of Pittsburgh, Pittsburgh, Pennsylvania 15260, USA

Received 6 March 1985; accepted for publication 2 July 1985

The reactive chemistry of methanol on the Cu(ll1) surface, both with and without preadsorbed

oxygen atoms, is investigated between 190 and 700 K. The clean Cu(ll1) surface is inert, and

molecularly adsorbed methanol, the only stable surface species identified on this surface, desorbs

at about 210 K. Various trends are examined as a function of oxygen coverage, from the clean

surface to the saturation oxygen coverage (approximately 0.45 0 atom/Cu atom). The capacity of

the surface to adsorb methanol (190 K), and the formaldehyde yield ( - 400-450 K) are both

maximized when the oxygen coverage is about 0.26 0 atom/Cu atom. Trends in the yield of other

products, and the temperature for decomposition of the stable methoxy intermediate are examined.

Also. the rate of methoxy decomposition is limited by C-H bond breaking as evidenced by a

deuterium kinetic isotope effect.(C-H versus C-D). A minor decomposition path for methanol on

0 + Cu(ll1) involves CO, formation, probably via a formate surface intermediate. Preadsorbed

oxygen serves as an acceptor of the methanol hydroxyl hydrogen, enabling facile methanol

conversion to methoxy at low oxygen coverage for T >, 190 K. However, at high oxygen coverage

(e 2 0.26 0 atom/Cu atom) oxygen inhibifs surface reactivity. A two-dimensional model which

defines three types of surface sites is used to explain the general trend of methanol reactivity as a

function of oxygen coverage.