Step Effects on the Dissociation of NO on Close-Packed Rhodium Surfaces

The dissociation paths and thermochemistry of nitric oxide (NO) on flat, close-packed Rh(111) and on stepped Rh(211) surfaces have been investigated. Self-consistent, periodic, density functional theory (DFT-GGA) calculations, using both PW91 and RPBE exchange-correlation functionals, have been employed to determine binding geometries and binding energies for the initial, intermediate, and final states, and for the transition states along each reaction pathway studied. The order of the calculated chemisorption energies for the atomic and molecular species, with the most stable listed first, is N 211 > N 111 > O 211 > O 111 > NO 211 > NO 111 . The effective activation energy barriers and the reaction energies for NO dissociation were also obtained for both Rh(111) and Rh(211). The presence of steps leads to an increase in the reaction exothermicity and to a decrease in the effective activation energy. A comparison between experimental data and these results suggests that NO dissociation at defect sites may dominate the process on close-packed Rh single crystal surfaces.