The reconstruction of Rh(001) upon oxygen adsorption

Abstract

We report on a first-principles study of the structure of O/Rh(001) at half a monolayer of oxygen coverage, performed using density-functional theory. We find that oxygen atoms sit at the center of the black squares of a chess-board, c(2 × 2), pattern. This structure is unstable against a rhomboid distortion of the black squares, which shortens the distance between an O atom and two of the four neighboring Rh atoms, while lengthening the distance with respect to the other two. We actually find that the surface energy is further lowered by allowing the O atom to get off the short diagonal of the rhombus so formed. We predict that the latter distortion is associated with an order-disorder transition, occurring below room temperature. The above rhomboid distortion of the square lattice may be seen as a rotation of the empty, white, squares. Our findings are at variance with recent claims based on STM images, according to which it is instead the black squares which would rotate. We argue that these images are indeed compatible with our predicted reconstruction pattern.

Importance of surface carbide formation on the activity and selectivity of Pd surfaces in the selective hydrogenation of acetylene

“…3) at the 0.5 monolayer (ML) coverage of the surface carbon over Pd(100). The clock-type surface reconstruction has been observed previously using both STM experiments and theoretical calculations on Rh(100) and Ni(100) upon adsorption of carbon, oxygen and nitrogen atoms [41][42][43][44][45][46][47].…”

Oxidation electronics: bond–band–barrier correlation and its applications

“…It is interesting to note that the Ni(100)-(2Â2)p4g-2N STM image exhibits two orientations of the depressions. With slight deviation, one is along the [10] direction and the In 1998, Alfe et al [160,161,277] suggested an alternative (Fig. 20d) for the Rh(001)-c(2Â2)p4g-2O second phase.…”

Structure sensitivity in the CO oxidation on rhodium: Effect of adsorbate coverages on oxidation kinetics on Rh(100) and Rh(111)

“…At low CO coverage all CO ads is inside the p(2ϫ2) and reacts to CO 2 between 300 and 400 K. At higher coverages of CO ads reaction occurs in the c(2ϫ2), with a sharp CO 2 formation peak at 280 K. We wonder if this peak is associated with the lifting of the well-documented clockwise-anticlockwise reconstruction of the Rh͑100͒ surface upon saturation with O. 32,[60][61][62] The splitting up of the 350 K CO 2 formation into a lower and a higher temperature CO 2 formation channel with increasing CO coverage as seen in the right part of Fig. 2 is due to depletion of oxygen atoms.…”