Formation of active sites on transition metals through reaction-driven migration of surface atoms.

Adopting low-index single-crystal surfaces as models for metal nanoparticle catalysts has been questioned by the experimental findings of adsorbate-induced formation of subnanometer clusters on several single-crystal surfaces. We used density functional theory calculations to elucidate the conditions that lead to cluster formation and show how adatom formation energies enable efficient screening of the conditions required for adsorbate-induced cluster formation. We studied a combination of eight face-centered cubic transition metals and 18 common surface intermediates and identified systems relevant to catalytic reactions, such as carbon monoxide (CO) oxidation and ammonia (NH) oxidation.

Crystallographic and spectroscopic character-ization of 4-nitro-2-(tri-fluoro-meth-yl)benzoic acid and 4-nitro-3-(tri-fluoro-meth-yl)benzoic acid.

The title compounds, both CHFNO, represent two isomers of nitro tri-fluoro-methyl benzoic acid. The compounds each contain a nitro functionality to the carb-oxy-lic acid group, with the tri-fluoro-methyl substituent to the acid group in the 2-isomer and to the nitro group in the 3-isomer. The regiochemistry with respect to the tri-fluoro-methyl group results in steric inter-actions that rotate the carb-oxy-lic acid group or the nitro group out of the aromatic plane in the 2- and 3-isomer, respectively.