Promoted activity of annealed Rh nanoclusters on thin films of AlO/NiAl(100) in the dehydrogenation of Methanol-d.

Annealed Rh nanoclusters on an ordered thin film of AlO/NiAl(100) were shown to exhibit a promoted reactivity toward the decomposition of methanol-d, under both ultrahigh vacuum and near-ambient-pressure conditions. The Rh clusters were grown with vapor deposition onto the AlO/NiAl(100) surface at 300 K and annealed to 700 K. The decomposition of methanol-d proceeded only through dehydrogenation, with CO and deuterium as products, on Rh clusters both as prepared and annealed.

Dependence on Size of Supported Rh Nanoclusters in the Dehydrogenation of Methanol- Obstructed by CO.

The size effect on the activity of a catalyst has been a focal issue since ideal catalysts were pursued, whereas that on the degradation of a catalyst, by reaction intermediates such as CO, is little discussed. We demonstrate that the dehydrogenation of methanol- on supported Rh nanoclusters precovered with CO (Rh clusters) was obstructed, indicated by a decreased production of CO and D; the obstructive effect exhibits a remarkable dependence on the cluster size, with a minimum at a cluster diameter near 1.4 nm.

Decomposition of methanol-d on Au-Rh bimetallic nanoclusters on a thin film of AlO/NiAl(100).

The decomposition of methanol-d4 that was adsorbed on Au-Rh bimetallic nanoclusters grown by the sequential deposition of Au and Rh vapors onto ordered thin-film Al2O3/NiAl(100) at 300 K, occurred by means of dehydrogenation and primarily on the surface Rh. Nevertheless, the surface Rh atoms were not equally reactive; their reactivity altered with both structural and electronic effects arising from the alloying. The Au deposited on Rh clusters decorated the surface and deactivated Rh by not only directly obstructing them but also by neighboring them.

Surface structures and compositions of Au-Rh bimetallic nanoclusters supported on thin-film AlO/NiAl(100) probed with CO.

The surface structures and compositions of Au-Rh bimetallic nanoclusters on an ordered thin film of AlO/NiAl(100) were investigated, primarily with infrared reflection absorption spectra and temperature-programmed desorption of CO as a probe molecule under ultrahigh-vacuum conditions and calculations based on density-functional theory. The bimetallic clusters were formed by sequential deposition of vapors of Au and Rh onto AlO/NiAl(100) at 300 K. Alloying in the clusters was active and proceeded toward a specific structure-a fcc phase, (100) orientation, and Rh core-Au shell structure, regardless of the order of metal deposition.

Formation and structures of Au-Rh bimetallic nanoclusters supported on a thin film of AlO/NiAl(100).

Self-organized alloying of Au with Rh in nanoclusters on an ordered thin film of AlO/NiAl(100) was investigated via various surface probe techniques under ultrahigh-vacuum conditions and calculations based on density-functional theory. The bimetallic clusters were formed on the sequential deposition of vapors of Au and Rh onto AlO/NiAl(100) at 300 K. The formation was more effective on the oxide seeded with Rh, since all post-deposited Au joined the pregrown Rh clusters; for metal deposition in the reverse order, some separate Rh clusters were formed.