Formation of ordered structures of NO on Rh(111)

Abstract

In this work, several ͑unreported͒ structures of NO on Rh͑111͒ are presented for coverages ranging from 0-0.78 ML. The formation of these structures as evidenced experimentally by scanning tunneling microscopy ͑STM͒ images is explained using density-functional theory derived values for the lateral interactions and adsorption energies of NO on Rh͑111͒. Kinetic Monte Carlo simulations using the derived lateral interactions are performed to determine structures at finite temperatures. The resulting structures can be directly compared to the molecular arrangements observed in the STM experiment. The configuration of the first three structures that form for increasing coverage is the same both experimentally and theoretically. In all three structures, the molecules only occupy the fcc and hcp adsorption sites. Yet, at high coverage, at which the top adsorption sites become occupied, a discrepancy arises.

High-Pressure NO-Induced Mixed Phase on Rh(111): Chemically Driven Replacement

“…The calculated CLSs of Rh 0 (−0.46 eV), Rh 1/3 (−0.27 eV), Rh 2/3 (+0.07 and +0.10 eV), and Rh 1 (+0.57 eV) are in good agreement with the experimental CLSs of −0.5, −0.2, +0.2, and +0.5 eV, respectively. Therefore, the present XPS results for the c (4 × 2)-2NO and p (2 × 2)-3NO phases support the previously proposed structure models formed under UHV conditions. − …”

“…According to the previous reports on this structure, two NO molecules are packed at the hcp- and fcc-hollow sites in a unit cell, resulting in a coverage of 0.50 monolayers (ML) with respect to the number of surface Rh atoms as shown in Figure d. ,,,, Further NO exposure causes a phase transformation to p (2 × 2), which is completed at 60 L as shown in Figure e, and the pattern no longer changes even under continuous dosing at 10 –7 Torr. NO molecules occupy the top sites above 0.5 ML. − It is noted that the present LEED observation cannot exclude coexistence of p (2 × 2)-2NO and p (2 × 2)-3NO structures. However, most of the p (2 × 2) overlayers contain three NO molecules in one unit cell as indicated by XPS results described later.…”

“…In this work, we studied NO adsorption behavior on a Rh(111) surface over wide pressure ranges from ultrahigh vacuum (UHV) to 1 Torr by the use of NAP-XPS and low energy electron diffraction (LEED). Experimental results are paralleled by computational simulations; that is, the results are interpreted on the basis of optimized geometries and CLSs for NO overlayers reported by the previous studies. − We found a formation of a mixed overlayer of NO and atomic oxygen (O) under a high-pressure condition. This mixed overlayer is formed via dissociation of NO and selective removal of atomic nitrogen (N).…”

“…According to the previous reports on this structure, two NO molecules are packed at the hcp-and fcc-hollow sites in a unit cell, resulting in a coverage of 0.50 monolayers (ML) with respect to the number of surface Rh atoms as shown in Figure 1d. 3,4,7,8,17 Further NO exposure causes a phase transformation to p(2 × 2), which is completed at 60 L as shown in Figure 1e, and the pattern no longer changes even under continuous dosing at 10 −7 Torr. NO molecules occupy the top sites above 0.5 ML.…”

“…Rhodium (Rh) is known as a good catalyst for the reduction of harmful nitroxides. The adsorption of nitric oxide (NO) on Rh surfaces has been studied extensively from both experimental and theoretical points of view. − Recently, high-pressure-induced formation of various high-density overlayers of simple molecules such as CO, NO, and O 2 , accompanied by surface restructuring and distinct catalytic activities on Pt-group metal surfaces, has been found using high-pressure surface science techniques. − …”