Interactions between co-adsorbed CO and H on a Rh(100) single crystal surface

Abstract

Co-adsorption of CO and H(2) on a Rh(100) single crystal surface has been studied by a combination of temperature programmed desorption (TPD), reflection absorption infrared spectroscopy (RAIRS), low energy electron diffraction (LEED), and density functional theory (DFT) calculations. Exposure of CO to a hydrogen precovered surfaces at 150 K results in some displacement of adsorbed hydrogen and a layer with 0.67 ML H and 0.67 ML CO is obtained. A c(3 square root(2) x square root(2))R45 degree structure is formed with CO occupying bridge sites and hydrogen occupying partly bridge sites on the surface and partly octahedral subsurface sites, causing hydrogen to desorb at temperatures around 230 K.

Methane Steam Reforming Kinetics for a Rhodium-Based Catalyst

“…Wei and Iglesia's study found an activation energy of 109 kJ/mol [18] for an assumed clean surface, which is not too far from what we found in this study. Maestri et al included coverage effects in determining the activation energy and estimated an activation energy of 62 kJ/mol at h CO = 0.15 and h H = 0.2, which corresponds well with our observed values that also include a partly coverage of CO and H. [29] and Rh(100) [30]. CO is preadsorbed at temperatures below -143°C for both sets of experiments.…”

“…Studies of coadsorption of CO and hydrogen on Rh(100) show that hydrogen is destabilised and that some of the hydrogen desorbs at a lower temperature [30]. When there are a low number of free sites, the surface will predominantly be covered by CO. Our model predicts that the coverages for the two species, CO and H, are similar at steam reforming conditions as shown on Fig.…”

“…On single crystal closed packed surfaces, CO are adsorbed on Ru(0001) [29] and Rh(100) [30]. The experimental conditions are almost equal, making ground for a fair comparison.…”

Weakly-bound hydrogen on defected Pt(111)

“…4). CO-induced penetration of H atoms into subsurface interstitial sites has been reported on Pd(111) [77] and Rh(100) [78]. Kobayashi et al [80] recently reported hydrogen absorption by 1.5 ± 0.5 nm-sized iridium nanoparticles up to 0.18 H per Pt atom at 303 K and atmospheric pressure of H 2 .…”

The interaction of CO molecules on Au–Rh bimetallic nanoclusters supported on a thin film of Al2O3/NiAl(100)

“…3b (rescaled CO IRAS spectra). 8,26,[76][77][78] The CO also adsorbed on top of the Rh atoms, as no absorption feature for CO on bridge or hollow sites, expected in the regime 1770-1900 cm À1 , 26,76-78 was observed. The much greater absorption intensity from CO Au does not correspond to much more numerous Au sites on the bimetallic clusters, but to the greater dipole moment for CO Au on the more electronegative Au, as indicated in the DFT calculation below.…”