A quantum chemical study of hydrogen adsorption on carbon-supported palladium clusters.

A key step for achieving better insight into catalytic hydrogenation reactions is to understand in detail the process of hydrogen adsorption on the catalyst. The present article focuses on hydrogen adsorption on carbon-supported palladium clusters, which are nowadays one of the most common catalysts in industrial applications. Density functional theory is applied to study Pd₆ and Pd₂₁ clusters to reveal the influence of the carbon support material on the properties of the catalyst as well as on the mechanisms and energetics of the hydrogen adsorption. In general, a stepwise hydrogen adsorption process is observed consisting of molecular adsorption followed by dissociative chemisorption. The carbon support material does not noticeably affect the reaction mechanisms, but has a large influence on energy barriers and preferential adsorption sites. Our comparison of Pd₆ and Pd₂₁ systems reveals that small clusters, such as Pd₆, are able to model some but not all important properties of palladium nanoparticles and, therefore, it is essential to also study larger cluster sizes. [ABSTRACT FROM AUTHOR]